Dr. Cotton, I'd just shown you those two photographs comparing the swatches in item 47 and item 12. Do you recall that?
Okay. Now, what I would like to do is just show you a computer graphic that was created, and I wanted to ask you some questions about it, Dr. Cotton.
All right. Dr. Cotton, what I would like you to do for the purposes of this demonstration visualization is assume that that red rectangle is a swatch, a bloodstain swatch. Obviously a bloodstain swatch is much, much smaller than that, right, Dr. Cotton?
Okey-doke. And in the illustration, Dr. Cotton, this is a blood swatch representing the bloodstain on it coming from person 1. And on that blood swatch, I have placed a number 1 four times to suggest a certain quantity, whatever it is, of DNA present in that swatch.
Now, would you agree, Dr. Cotton, that sealing that swatch in a plastic bag, if it is moist, if the swatch itself is still wet, can cause degradation of the DNA?
And that--okay. And putting it in a plastic bag as opposed to a paper bag, for instance, enhances that degradation; isn't that correct?
I don't think that, again, for the short term, it's going to make any difference. For a longer term, it would.
And when you say it would, it would make a difference whether it's packaged in a plastic bag as opposed to say a brown paper bag?
And if you added to that plastic bag the factor of heat, the element of heat, would that even further enhance the degradation?
And again, just to reiterate what I think you're already said, that as long as the blood swatch remains moist, that degradation will continue; is that correct?
I'm going to object at this point as to foundation and relevance. Assuming facts not in evidence.
And I think finally here, the last element that you talked about before was the factor called time. And the longer the blood swatch is wet and remains in that plastic bag and subjected to heat and moisture, the more it will degrade.
Excuse me, your Honor. I'm going to enter another objection under 352 as to misleading. As far as the graphics is what I'm referring to.
And you said, Dr. Cotton, I believe yesterday that it is possible that the DNA can become so degraded in the swatch that although the swatch still appears red, it will have no identifiable DNA in it or human DNA in it; is that correct? That's possible?
Over a very long period of--in order for it to not have--you won't get to the point where you don't have small bits of DNA, but you can get to the point where the degradation is so substantial that you can't easily measure it by the methods that are generally used in a forensic laboratory.
So what we're really talking about is the DNA's detectability. That's what lost through time, moisture, heat?
Now, take that blood swatch which has now been completely degraded and assume for a moment that it is cross-contaminated with another--
Now, assume that the degradation was so complete, as you just described it, that the DNA was no longer detectable.
If you ran a DNA test on it under those circumstances, you would get, I believe you said, no result; is that correct?
Depending on the level of degradation, it can be so degraded that you don't get an RFLP result, and if the level of degradation can become so much, that you won't even get a PCR result.
Now, if you take that blood swatch originally that came from person 1 and you brought it into actual contact with a wet blood swatch from person 2, all with fresh blood from person 2, could that cause cross-contamination as to the blood swatch that originally had the sample from person 1?
If the hypothetical is as you're suggesting where you have a blood swatch and it no longer has typeable DNA from person 1 and somehow it comes into contact with a second swatch that's wet in such a way that they are so closely connected as to transfer a sufficient amount of DNA to be typed or a liquid blood sample--and same thing. You have to transfer a sufficient amount of DNA to be typed--then of course your hypothetical would be correct.
And by the way, Dr. Cotton, I think you said, for instance, in sample 52, there was approximately 25 nanograms of DNA present in that--in that--for that DNA test; is that right?
What I--what I said about sample 52 was--are you asking me about the RFLP result or the PCR result?
I asked you about the RFLP result, to estimate approximately how much DNA was loaded in the lane. Wasn't your initial testimony that there was approximately 25 nanograms of DNA in that lane?
That is correct, and that is what I said yesterday. What I said yesterday, however, wasn't completely precise, and I can clarify it if you wish me to.
When I made an estimation that there was 25 to 50 nanograms of DNA for the RFLP result, what--what I was doing in my head was saying, if I compared--and these things have been done in the lab. So I have some mental image of this. If I took a known sample of specific quantities of DNA that was in good condition and I loaded different amounts on a gel, the intensity of the banding pattern that I'm seeing from item 52 is about the same as I might expect to see for--for 25 to 50 nanograms. Now, if you look at the DNA in item 52 on the small gel as it was originally--on the mini gel to see how degraded it was, you see that there's DNA all the way from the top of the gel all the way on down, meaning it's quite degraded. Only the only the high mole--only the big pieces of DNA--
Yes. Only the big pieces of DNA of that--out of that sample can participate in the RFLP pattern. So whereas it's clear that there's mass wise, that is total quantity from the slot blot, there is more than 25 or 50 nanograms. What I was telling you was that the pattern--
What I was telling you is that the pattern was the equivalent of 25 or 50 nanograms of DNA that's in good condition. So more DNA existed in that whole sample, but the amount that could be participating in the RFLP had to be that portion that was in good enough condition, and that would have been some much smaller portion than the whole sample.
And, Dr. Cotton, when you described that--was it a yield gel where the DNA is spread out along the whole length of it?
On the yield gel test--and correct me if I'm mistaken--you will not be able to distinguish bacterial DNA that is present from human DNA; is that correct.
Okay. Now, getting back then to the illustration in this particular slide, if sufficient quantity of either fresh blood from a reference sample or--
Now, in this example that I put up there, slide I, you have a situation where the initial swatch has now been cross-contaminated with biological material from person number 2. Do you see that?
Right. And that's--the three 2's is simply to indicate that much more of person 2's DNA is on that swatch than person 1's.
Now, if under this hypothetical, if you were then to do a DNA test, for instance, an RFLP test on a swatch that went through this process, wouldn't the RFLP test give you a profile of a person 2 rather than person 1?
And if the degradation was sufficiently complete as to person 1, wouldn't it also give you a PCR result for person 2 as opposed to person 1?
Thank you. Now, one of the things I believe you said on direct examination, Dr. Cotton, was that the presence of soil and leaves mixing with the bloodstain can cause degradation; is that correct?
And, Dr. Cotton, would you come down and take a quick look at what is known as item 47, which is photo id no. 112? Do you see it?
Okay. Do you see with your naked eye any small pieces of anything on the bloodstain?
Okay. And actually as to--all right. You can have your seat again. Thank you, Dr. Cotton.
Mr. Neufeld, I would suggest that you and Mr. Scheck show the graphic to all the jurors so they can see the close-up of that item.
And, Dr. Cotton, you mentioned on direct examination that one way to assess if there's going to be an interference with the DNA typing is to do what's called a substrate control; is that correct?
I don't--I wouldn't use the term "Interference." Umm, it just--it only tells you whether or not there was any DNA close to where the stain was taken from.
Well, doesn't the substrate control also tell you something about the nature of the substrate?
And so the term "Substrate control" refers to taking a control swatch, wet swatch of the actual material that the stain is on; isn't that right?
And one piece of information that that substrate control can give you as an examiner is to tell you something about the condition of the substrate, whether or not there are other chemicals present for instance?
It doesn't--you're not testing for any other chemicals. The only thing you're testing for is the presence of human DNA, and the only way you detect that is if you have a type. So the only thing in--for purposes of DNA, the only thing that substrate control is telling you is whether you had any other human DNA in a position where the substrate control was taken adjacent to the stain.
Dr. Cotton, through Mr. Clarke's hypothetical, asking whether or not certain samples could be degraded as a result of their contact with soil and leaf stains or leaf material, what I'm asking you is, if the substrate control is taken right next to the bloodstain, could that be a useful indication or provider of information to see whether or not the swatch right next to the stain has soil on it or leaf stains? Would that be something that you could look at?
You could look at it with your eyes and you could say, well, it's green or it's brown or whatever, but that's not any kind of scientific procedure to tell you what was on that substrate and then been transferred to the substrate control. You'd have to do some other kind of test.
So there is testing that could be done to determine whether or not there is soil present on that control?
Well, the presumption is, it's the bacteria in the soil that's causing the degradation.
So if the stains were brought into contact not only with the sealed plastic bag and heat and moisture over a period of time, but also soil, the combined effect of all those different factors can further enhance degradation than if there was no soil present?
And, Dr. Cotton, has there been any research done as to whether or not soil can inhibit the analyst's ability to detect DNA in a specimen, in a biological specimen?
As far as I know, it's not going to inhibit your ability to detect it in terms of--for example, like a slot blot, you could say it's here. It might inhibit your ability to type it if there's a lot of degradation.
So you're saying that soil only will degrade DNA, but it doesn't have this independent effect, namely of simply inhibiting the ability to--to type it?
No. I said it might inhibit your ability to type it, but it wouldn't necessarily inhibit your ability to detect it.
Now, there's already been testimony in this case, Dr. Cotton, about the amount of blood in the blood vial containing Mr. Simpson's reference sample. I wish to ask you a hypothetical question. If 1.5 milliliters of Mr. Simpson's reference sample was unaccounted for in that vial, approximately how many microliters of blood would that be able to produce?
You talked on direct examination, Dr. Cotton, about the special sensitivity of DNA typing. Do you recall that?
I recall talking about issues of what tests were more sensitive than what other tests.
And you also talked about some of the safeguards that are necessary because of the particular sensitivity of PCR amplification. Do you recall that?
And would you agree that given the exquisite sensitivity of PCR amplification, it is essential that even greater safeguards be taken to avoid contaminating evidence collected than would ordinarily be used?
Why don't you rephrase that question? The concern is the term "Exquisite" is without definition at this point.
Have you ever heard the term "Exquisite sensitivity" applied to PCR amplification?
I don't know that I've heard that particular term.
"Exquisite" isn't something you would normally see in the scientific nomenclature.
Well, how about extraordinary sensitivity? Would that be more appropriate to describe what happens to PCR amplification?
It's very sensitive. To me, it doesn't seem extraordinary giving--given what we know about how well the reaction works. But if you compare it to other tests, then it is much more sensitive than other types of tests.
And as a result of that much, much greater sensitivity, would you agree that it's essential to have even greater safeguards to prevent any kind of cross-contamination of the evidence collected?
Would you agree that special safeguards have to be taken in collecting biological specimens to avoid cross-contamination given the heightened and extreme sensitivity of the PCR amplification test?
I don't know about how evidence is collected at a scene. So I'm having trouble with the question.
Even without knowing how it's collected at a scene, but knowing how sensitive PCR typing is and based on your expertise as a molecular biologist and as a forensic scientist, would you agree that special safeguards have to be taken in the collection and preservation of biological specimens that are intended to be subjected to PCR amplification?
When you use the term "Special"--when the evidence is collected and--it should be handled in a way to minimize contamination. When you saw should you take special safeguards, I would expect that the same safeguards would be applied whether you were doing serology or RFLP or PCR. You don't want contamination between samples regardless of what kind of testing that you're using.
In your laboratory, Dr. Cotton, isn't it true that over and above the safeguards and controls that you use for RFLP testing, you have additional safeguards for PCR testing?
Yes, that's true. But the--many of those safeguards are now because in the laboratory, there is the existence of amplified product. And, therefore--which isn't going to be out where evidence is collected. So many of those extra safeguards are designed so that you can not get amplified product back to your original sample. Now, that's not a hundred percent of them, but that's a good part of them.
And by the way, in your laboratory, to avoid the possibility of getting that amplified product back to the original location, I believe you said that you have a series of different rooms that the item of evidence moves through and it's a one-way street; is that correct?
Do you have any knowledge, Dr. Cotton, as to whether or not the Los Angeles Police Department laboratory--
The PCR amplification test that you utilize doesn't have the capacity to discriminate whether it's amplifying the original target DNA or a subsequent cross contaminant; isn't that correct?
And since it doesn't have that capacity, Dr. Cotton, would you agree that even a minute contaminant could be amplified perhaps a million times or more during the amplification process?
Well, as a scientist, Dr. Cotton, have you ever heard the expression, "Garbage in, garbage out"?
Well, in your laboratory, have you been taught and have you taught others that while working with a bloodstain, one shouldn't do anything which could leave even a minute portion of the stain on your clothing so as to risk cross-contamination?
And does your laboratory in fact have a written manual to spell out the safeguards that must be followed to reduce the chances of cross-contamination in your laboratory?
Yes. Those procedures that are designed to reduce cross-contamination are laid out in the standard operating procedure.
And is everyone in the laboratory who handles biological material required to be familiar with those written safeguards?
Everyone in the laboratory who handles evidence is required to be aware and follow those safeguards.
In terms of our laboratory, they are mandatory. We're not just saying we hope you'll do a particular thing. We're saying we will all do this particular thing.
Now, in this case, there's been testimony by Gregory Matheson that the criminalists at the Los Angeles Police Department are not required to change their gloves in between the handling of each piece of evidence.
And you've already--she has no idea about the handling, packaging, collection of the evidence. We've established that. Let's move on.
May I ask questions that occurred at the laboratory as opposed to at the crime scene and ask her opinion as an expert?
At Cellmark diagnostics laboratory, Dr. Cotton, is glove changing between each item required to avoid any kind of cross-contamination?
Well, if a molecular biologist at Cellmark handles one item of evidence, let's say 47, for instance, in our case and does some manipulation with the item using different pieces of equipment and then packs up that item and now takes out a second item of evidence, is the molecular biologist at Cellmark required to change his or her gloves before moving on to the next item?
They're not required to and they normally--if they haven't touched the item with their gloves, that is, if they've handled it with forceps or a scalpel or something and they haven't touched it, then they may not change their gloves in between handling the first item and the second item.
Referring you--you have a protocol you said that has been prepared by Cellmark for the use of all personnel that handles biological items of evidence in the laboratory; is that correct?
Dr. Cotton, and there's a section in your written protocol dealing with the handling of evidence during preparation for analysis; isn't that correct?
Isn't it a fact, Dr. Cotton, that in that protocol, it states, quote, "Clean disposable gloves must be worn when handling evidence samples. To avoid cross-contamination of evidence, gloves are changed between samples," closed quotes?
KEY QUOTEAt Cellmark, are the scientists instructed in writing to change the bench paper that is used in manipulating samples in between the handling of each sample?
And at Cellmark, Dr. Cotton, when your technicians and electrobiologists--your scientists--excuse me--when your scientists manipulate the items with pieces of equipment, isn't it required that they either dispose of the equipment between items or put it into a beaker of bleach?
They will either dispose of it if it's a disposable piece of equipment or they will clean it with bleach or alcohol.
And would you agree, Dr. Cotton, that bleach is a very effect--is very effective at instantly degrading DNA, that is, in breaking it down?
And would you agree, Dr. Cotton, that simply wiping a piece of equipment with a chem-wipe or distilled water will not be as effective as either disposing of the equipment or dropping it into a beaker of bleach?
I would prefer wiping it down with bleach or alcohol as opposed to wiping it down with water. Wiping it down with water is better than not wiping it down at all.
Well, granted. But you would agree, Dr. Cotton, that if you're really concerned with getting rid of any lingering DNA or biological material that may be invisible to the naked eye on a piece of equipment, bleach is a far better tool for doing that than simple distilled water?
Well, remember, at that point, you don't have naked DNA. I mean, you still got cells there, and the bleach has to get to the DNA in order to destroy it. So it may be just as effective or may not. I don't really know.
Do you know anything at all, Dr. Cotton, about whether or not water alone will kill and degrade DNA?
Okay. Another point that you made, Dr. Cotton, I believe on direct examination is that it is important not to rush these tests; is that correct?
Well, I think you said to Mr. Clarke that if you had no other cases going on in the laboratory and you were conducting a PCR test from beginning to end, in other words, from the moment you received the samples from an outside law enforcement agency until you get the dots on the strips, that you could get results in as little as a few days I believe you said. And if it's not a few days, please correct me.
No. You could get resu--well, if you worked a really long day, you could start one sample at the beginning and get results by the end.
Well, it's--you know, depends on what kind of DNA extraction you do. Some of them are shorter than others. So if you do a short one and then you set up your amplification--so say your short one took an hour, your amplification set-up takes a half hour, your amplification takes about two and a half hours, what is that? Up to four or so. And then the typing itself takes about two more hours. So--and given that you're taking some pauses in between, if you worked all day, you could get--and you didn't have anything else to do, you could get a type--if you started in the morning, you could get a type by the end of the day.
Have you ever done PCR typing on evidence specimens in groups of a dozen that quickly in your laboratory in actual casework?
Now, you said that at Cellmark I believe, the room where the evidence is handled, I think you referred to it as, quote, a biological safety cabinet, unquote. Was that the term you used?
No. What--what I said was that the DNA extraction was done in a biological safety cabinet. And it's not a room. It's a--it's a thing. It's a piece of equipment.
And does that hood prevent air flow from outside the cabinet area from coming inside the cabinet area?
And what is the reason that you want to prevent air from outside the cabinet area coming inside the cabinet area where you're doing the extractions?
Well, in reality--it also prevents what's inside the cabinet from coming outside. And the first reason to use the cabinet is the protection of the analyst because, as most of you probably know, blood samples can contain viruses that can be very harmful. So first reason is to protect the analyst. Second reason is to protect the evidence.
And when you say, "Protect the evidence," you want to avoid again cross-contamination with this--this biological cabinet; isn't that correct?
Yes. It's the area in which the DNA extraction is done. It's not the area--for example, if they--uh, they may handle evidence outside on the bench. For example, they wouldn't handle a hair in the biological safety cabinet because the air flow is sufficient that you might blow it away. So you wouldn't want to do that.
Thank you. Have you ever inspected the Los Angeles Police Department SID laboratory?
And in your laboratory, to avoid cross-contamination, do you do your extractions on evidence at a separate time and place than when you do your DNA extractions on a reference sample?
And when you say a separate time, how much time is there separated between the extractions?
Well, it could be just a matter of minutes if you did one, put it away and then got the other one out, or it could be a matter of days or months, depending on when the various items were actually received.
And do you keep the extraction of the reference sample separate from the other extractions until you get to the amplification stage?
We did that--we set that up in response to the results that we got on the second group of CACLD proficiency tests where we clearly had some contamination that we couldn't determine precisely where it came from.
KEY QUOTEWould it be fair to say that one danger of doing the extraction on the reference sample at the same time that you do the extraction on the various items of evidence is that you could get cross-contamination from the much more enriched DNA in the reference sample?
And as a result of that kind of cross-contamination from the more enriched reference sample, couldn't that lead to a false positive in the evidentiary specimens?
Okay. Now--by the way, Dr. Cotton, under your own laboratory's procedures, would you extract two different--would you extract samples from two different crime scenes at the same time as one another?
If you were told by the submitting agency, Dr. Cotton, that samples from one location--that samples from one location had much more DNA than samples from the other location, would that influence your decision to extract those samples separately?
Well, in general--the answer is no because--but it's because people are asking us to do the DNA test. They're not ever telling us, "You have this much DNA. So now go do your DNA test." Usually we are getting samples because the submitting agency doesn't have the same capabilities as we do.
Well, would you like to know before you decide whether these samples should be extracted together or separately whether some of the samples have much more blood on them than other samples?
Well, you might like to know that, but that's almost all the time not possible to know unless you're looking at the physical size. You have a stain that's a foot versus a stain that's an inch, obviously it's likely that the big one will have more than the little one. But apart--and then you wouldn't use the whole big one anyway. You would cut out a small piece. So--
So most of the time, you simply can't know that because you don't know how much DNA there is on the stain just by looking at it.
For instance, in this case, Dr. Cotton, there's been testimony that when item 12 was collected from inside the foyer of Mr. Simpson's home, there was a collection of three drops of blood as opposed to the stains at Bundy, which were taken from a single drop of blood. Is that a factor that you might wish to know or might consider in determining whether or not the extraction should be done at the same time or done separately?
Just to go back one step for a moment, Dr. Cotton, you were mentioning the laminal flow hood that you have in the room where you do the extraction for DNA?
Is the purpose of that laminal flow hood to create literally a wall of air which separates the rest of the room from that work area?
It's not the purpose of a laminal flow hood to simply pull air from the lab into the work area and then outside, is it?
Dr. Cotton, you said sometimes the submitting agency can't give you information about relative quantities of DNA because that's why they're submitting it to you for testing; is that correct?
But there have also been instances, have there not, Dr. Cotton, where the submitting agency itself has conducted DNA testing on the same items or some of the same items even before it is given to you? Isn't that correct?
And do you know whether in this case, LAPD had in fact conducted DNA testing on some of the same items that they gave to you before they sent them to you?
I'm vaguely aware that they may have done some testing. I don't have any information on what items--that I recall having anyway, on what items had been or had not been tested. We did not--
Well, assume for purpose of this hypothetical that the Los Angeles Police Department had in fact the--as of June 14th, run PCR tests on every single one of the Bundy drops.
All right. Assume hypothetically, for purpose of this hypothetical, that the Los Angeles Police Department had run PCR testing on items 47, 48, 49, 50 and 52. Okay?
Assume for the purpose of this hypothetical that the Los Angeles Police Department had run PCR testing from beginning to end on items 47, 48, 49, 50 and 52 before--
Dr. Cotton, if a laboratory had done PCR typing on the samples that they were submitting to you, wouldn't you want that laboratory to provide you with as much information as possible about the quality and quantity of those samples?
It really probably wouldn't make any difference because we would be doing that assessment as we went along.
Well, would you agree that you do not want to process or do extractions at the same time of samples that have very, very little DNA with samples that may have relatively large amounts of DNA? Would you agree with that?
If there was a way to know that, then--and depending on the differences in amounts--
--you might try to not do the extractions at the same time. But for the most part, there isn't a way to know that and--never--I'll stop there.
So if the submitting agency had done some of those tests to quantify and to give a qualitative assessment of the DNA, wouldn't that be useful information for you to have in advance if in fact some of the samples had much more DNA than other samples?
Sustained. Did you have any information about any prior testing in this case prior to Cellmark doing its testing.
With the exception of the DOJ samples that we got as extracted DNA. We did receive information on quantitations on those samples.
When you say you didn't receive any information, Dr. Cotton, you're not saying there wasn't any information. You're just saying that nothing was communicated to you; is that correct?
In fact, Dr. Cotton, doesn't the user's guide, the manufacturer's user's guide for the kits that you use for PCR typing explicitly state that to perform DNA extractions from samples containing high levels of DNA separately from those samples containing low levels of DNA?
It may say that in there. I don't remember exactly, but--you know, it's a pretty big book. But I wouldn't be surprised.
And if it said that in bold type in the book, would you take that to mean that that was the strong recommendation of the manufacturer of the kit that you're relying on?
It might be the strong man recommendation of the manufacturer of the kit. However, the manufacturer of the kit is not a group that's engaged in routine forensic DNA typing. So --
So a laboratory with some experience might--like any recommendation, might decide to accept that recommendation or not accept it.
Isn't there a statement actually on the kit by the manufacturer that this kit is designed for forensic application?
Isn't the kit explicitly and expressly warranted to work only if you follow the directions on the kit? Isn't that a warranty given by the manufacturer?
Yes. But that's in terms of the salt solution concentrations and the temperature and the quantitation, that is the amount of DNA you add. There's no specific directions they can give you to ensure that the rest of your handling is good or bad. They can only tell you if you have the thing at 60 degrees, it will work, and if you don't, it won't.
So is it just--so I'm clear on this, is it your position that the expressed instruction from the manufacturer that you are, quote, "To perform DNA extractions from samples containing high levels of DNA separately from samples containing a low level of DNA" is something that the people who utilize this kit are free to ignore?
Yes. And I mean there--what's high and what's low? I mean, this is going to be the judgment of the people in the laboratory. That's not a specific instruction. It's a vague instruction.
KEY QUOTEGranted, Dr. Cotton, what's high and what's low is something that has to be determined by the particular laboratory. But once that assessment is made as to what is high and what is low, wouldn't you agree that it's critically important to follow the instruction that once--that that what you consider a high level of DNA should not be extracted at the same time with that what you consider a low level of DNA?
Overruled. We have asked this question. Again, I'll allow the question and answer one last time.
I have stated I think earlier that when--depending on how great a difference in amount of DNA you have, if it's a very great difference, then one would prefer if you were able to know ahead of time to deal with the large amounts of DNA or evidence that had a large amount of material on it separately from the smaller amount, and that's a relative decision for any specific laboratory.
Is the manufacturer of the kit the same entity that designed the validation studies for that kit?
Well, they certainly did a lot of validation studies, but they are not the only group that did validation studies using that kit.
Now, you mentioned in terms of your testing of items in this case that one of the items you were asked to do DNA profiling was the steering wheel inside the Bronco; is that right?
Uh, from one item of evidence, from the--I don't know if there's more than one item of evidence from the steering wheel. So--we had an item of evidence from the steering wheel.
And that one item of evidence was a blood swatch taken from a smear on the steering wheel; is that correct?
Now, would you agree, Dr. Cotton, that interpreting mixed stains is a more demanding challenge to the forensic laboratory than interpreting a stain that only has a single source?
And when you see more than two versions of a particular gene, that enables you to determine that there's more than one contributor to that stain, correct?
However, if you see three or four versions of the gene, you can't necessarily tell whether there's been two contributors or three contributors or more contributors; isn't that correct?
And with respect to the stain removed from the steering wheel of Mr. Simpson's Bronco, your DQ-Alpha typing method showed the presence of three different alleles; is that correct?
And I think you said yesterday, the day before that and the day before that one should only inherit two versions of a gene; isn't that correct?
All right. So certainly, Dr. Cotton, each of the individuals who you typed in this case as reference samples, namely, Mr. Simpson, Nicole Brown Simpson and Ronald Goldman, each had only two alleles for the DQ-Alpha marker?
And when you typed the DQ-Alpha markers--I'm sorry. When you typed that stain on the steering wheel, you found that there were three separate DNA types, correct?
And initially on this board that you saw, the Prosecution had written that the only one of the three people not excluded was Mr. Simpson, correct?
But I take it you did not help the Prosecution prepare this exhibit board, did you?
I saw some of the boards to make sure that they were right and I don't know if I--I--I don't remember if I saw this one. I may have. I might have.
Fine. Well, actually on the poly-marker data if you look at it, isn't every different version of every poly-marker included in this mixture?
Yes. You're correct. There are--all the possible alleles for the poly-marker are present in that sample.
So in fact, if you just looked at the poly-markers and nothing else in this case, you would have to say that there would be almost no useful information in the poly-marker results because the entire human population could have contributed to that mixture?
Assum--yeah, assuming all the intensities were--of the dots were--assuming the dot intensities weren't informative, and I don't recall that they are.
Okay. So the key information here in this particular case for you was not the poly-marker results, but rather DQ-Alpha results?
Yes. And not only were you able to not exclude Mr. Simpson, but you were not able to exclude Nicole Brown Simpson; isn't that right?
Meaning that she inherited the same version of the gene from her mother and her father?
And so because you see the 1.1 allele present in this mixture, that 1.1 allele could simply be two copies of--of the DQ-Alpha typing from Nicole Brown Simpson?
However, you in fact excluded Ronald Goldman as a contributor to this mixture; isn't that correct?
And the reason you excluded Mr. Goldberg as a contributor to this mixture is that Ronald Goldman is of a type 1.3, 4, correct?
And what that means is is that Ronald Goldman, his DQ-Alpha type has two alleles in it which are different from one another, correct?
And so if this sample contained a portion of Ronald Goldman's blood or biological material, you would also expect to see the 1.3 allele and not just the 4 allele?
And it was on the basis of that that you excluded Ronald Goldman as being one of the contributors to this mixture?
So would you agree, Dr. Cotton, that based on your analysis, that the number 4 allele that you see present in this mixture from the steering wheel must come from someone other than Mr. O.J. Simpson, Nicole Simpson Brown and Ronald Goldman? Isn't that correct?
Mr. Scheck, perhaps we ought to move that over here because that one height wise is hard to see unless it's in the middle.
All right. Mr. Scheck, you may need to--Mr. Scheck, don't go away. You may need to steady that.
You can do better than that. Can't you make it straight? Only a Californian could teach a New Yorker how to do that.
All right. Dr. Cotton, now, this third person who cannot be Mr. Goldberg and cannot be Nicole Simpson, Nicole Brown Simpson and could not be Ronald Goldman, who has--we'll call him--all right. We'll call him actually the fourth person because he's none of the three people whose reference samples you tested, all right?
This fourth person has the 4 allele, correct, has one of his two or one of her two alleles, correct?
Now, this person who has the 4 allele also has two alleles, inherited one from his mother and one from his father or one from her mother and one from her father, correct?
This person could be, given the presence of the 1.1 and 1.2, could have as a genotype a 1.1, 4, correct?
This person could have as a--I'll move in a second. I'm sorry. This person could have as a genotype a 1.2, 4. Woops. All right. A 1.2, 4, correct?
And this person--and this person could also have inherited the same version of the gene from both parents and be a 4,4, correct?
Okay. And those are three possible explanations for a genotype for a third--for a fourth person if the fourth person contributed the number 4 allele, correct? Those are the possible--
Those are the three possible--those are the three possible genotypes for a person in that mixture if that person's first allele is a 4.
Now, Dr. Cotton, I'm going to ask you a hypothetical, and I'm going to ask you whether or not that hypothetical is consistent or inconsistent with the observed evidence in your laboratory. Assume that Mr. Simpson cut himself in his home and walked out to the Bronco to get something from his car and bled in his own Bronco.
And assume, Dr. Cotton, that some other person other than Mr. Goldman, other than Nicole Brown Simpson, other than O.J. Simpson had come into contact with the blood of Nicole Brown Simpson and then entered that Bronco and made a smear on the steering wheel, having touched Mr. Simpson's blood--
Dr. Cotton, if somebody else who is either a type--a DNA type 4, 1.1 or 4, 1.2 or 4, 4 touched Mr. Simpson's blood and touched Nicole Brown Simpson's blood and touched that steering wheel, would that be consistent with the stain you found on the wheel?
Yes. And I mean there--what's high and what's low? I mean, this is going to be the judgment of the people in the laboratory. That's not a specific instruction. It's a vague instruction.
We did that--we set that up in response to the results that we got on the second group of CACLD proficiency tests where we clearly had some contamination that we couldn't determine precisely where it came from.
Yes. There are--all the possible alleles for the poly-marker are present in that sample.
Isn't it a fact, Dr. Cotton, that in that protocol, it states, quote, 'Clean disposable gloves must be worn when handling evidence samples. To avoid cross-contamination of evidence, gloves are changed between samples,' closed quotes?
Yes, it could.