Cross-examination of Dr. John Gerdes (part 4)

📄 Cross-examination of Dr. John Gerdes (part 4) — Friday, August 4, 1995

Address:

C:\DEPT103\CRIMINAL\1995\AUG\4\CROSS-EXAMINATION-OF-DR-JOHN-G.DOC

TRIAL

▲ Day 129 of 167

Witness: Dr. John Gerdes
Examiner: George Clarke
Called by: Defense • Date: Friday, August 4, 1995 • Utterances: 34

George Clarke cross-examines Dr. John Gerdes on the limitations and reliability of his contamination analysis of the LAPD crime lab. Clarke methodically establishes that many of Gerdes' 'contaminant' notations were based on faint, difficult-to-see dots, that Gerdes reviewed fewer than 100 casework samples, and — critically — that Gerdes could not actually conclude contamination from any casework (evidence) sample because he didn't know the sample's collection history. Two photographs are introduced as People's 566 and 567 at the close of the excerpt.

# 1 MR. CLARKE:

Incidentally, when you made changes, does that mean that there were mistakes that you made before that?

# 2 DR. GERDES:

Not necessarily.

# 3 MR. CLARKE:

Were there any instances in which you found that you had made mistakes in your chart?

# 4 DR. GERDES:

There were instances on the first time or in the particular light there were faint--faint, I guess what the DOJ would call hints, that later on I would look back and I would have to make a decision as to whether or not that was real. And basically what I would do on the first run through is just note those areas where I had questions and I would go back and look at those. I mean, it was never recorded as an absolute result until the final report. They were recorded as questionable, look at this one, look at it again, go back until you finalize it.

# 5 MR. CLARKE:

Isn't it true that in many instances of the various notations that you made on your chart about, quote, "Contaminants," that those included very faint dots?

# 6 DR. GERDES:

There are faint dots on--I wouldn't say many, but on a--on a significant proportion of those perhaps, yes.

# 7 MR. CLARKE:

Some of them were very hard to see; isn't that true?

# 8 DR. GERDES:

Yes. And recall, most of those were recorded by the analyst, and I, as a second analyst, am at a disadvantage in that these strips fade after they dry, and so the analyst might have seen those at darker intensity than I could.

KEY QUOTE

# 9 MR. CLARKE:

How many case work samples did you review in this study of the May, `93, through August of `94, review?

# 10 DR. GERDES:

There are substantial fewer case work samples.

# 11 MR. CLARKE:

Can you give us a number or an approximate number?

# 12 DR. GERDES:

An approximate number would be less than ten percent.

KEY QUOTE

# 13 MR. CLARKE:

So what number would that be, something under--

# 14 DR. GERDES:

Less than a hundred.

# 15 MR. CLARKE:

So something under a hundred case work samples?

# 16 DR. GERDES:

Yes.

# 17 MR. CLARKE:

Of the number of case work samples that you look at, how many did you determine in your opinion showed contamination?

# 18 DR. GERDES:

I didn't include case work samples unless they were known reference samples or the positive controls or the negative controls.

# 19 MR. CLARKE:

Is it your testimony that you can't determine from a case work sample whether or not there is contamination present?

# 20 DR. GERDES:

That is true, because I don't know where that sample came from or what conditions it was collected--under which conditions it was collected, so it would be unfair to count those because it is not defined as having come from a single individual.

KEY QUOTE

# 21 MR. CLARKE:

So is it true that any case work sample, you cannot conclude there was contamination because you don't know the history of the sample?

# 22 DR. GERDES:

It is true on those samples that are recorded as being evidence items. It is not true on the negative control or the extraction--the reagent blank or the positive control or items that were defined as being reference samples from a given individual.

# 23 MR. CLARKE:

The samples tested in this case were evidence samples, correct?

KEY QUOTE

# 24 DR. GERDES:

Yes.

# 25 MR. CLARKE:

And they were known samples from known individuals?

# 26 DR. GERDES:

Yes.

# 27 MR. CLARKE:

And then there were a series of controls you previously described, correct?

# 28 DR. GERDES:

That's correct.

# 29 MR. CLARKE:

All right. Your Honor, I have two photographs that I would ask to be marked as the next two exhibits.

# 30 THE COURT:

566 and 67.

# 31 (Peo's 566 for id = photograph) (Peo's 567 for id = photograph)

# 32 THE COURT:

Have you shown those to Mr. Scheck?

# 33 MR. CLARKE:

Yes.

# 34 (Brief pause.)

Temperature

procedural

Key Quotes (4)

Dr. John Gerdes

That is true, because I don't know where that sample came from or what conditions it was collected--under which conditions it was collected, so it would be unfair to count those because it is not defined as having come from a single individual.

Clarke gets Gerdes to concede he cannot actually prove contamination in any casework sample — a major concession that undermines the practical application of his entire lab analysis to the Simpson evidence.

Dr. John Gerdes

Yes. And recall, most of those were recorded by the analyst, and I, as a second analyst, am at a disadvantage in that these strips fade after they dry, and so the analyst might have seen those at darker intensity than I could.

Gerdes admits he was reviewing faded, degraded strips — weakening the authority of his contamination calls and suggesting his readings were less reliable than the original analyst's.

George Clarke

The samples tested in this case were evidence samples, correct? ... And they were known samples from known individuals?

Clarke pivots to establish that the Simpson case samples were exactly the type Gerdes just said he could not evaluate for contamination — setting up a logical trap.

Dr. John Gerdes

An approximate number would be less than ten percent.

Reveals Gerdes reviewed fewer than 100 casework samples — a small fraction — limiting the scope of his lab critique.

Evidence (3)

People's 566

Photograph (contents not described in transcript)

introduced and marked for identification

People's 567

Photograph (contents not described in transcript)

introduced and marked for identification

Informal

Gerdes' contamination chart with notations for faint dots and questionable results

discussed and challenged

Notable Exchanges (2)

George Clarke•Dr. John Gerdes

Clarke walks Gerdes through a logical trap: Gerdes admits he cannot determine contamination from casework samples because he doesn't know their history — then Clarke immediately confirms that the Simpson case samples were in fact casework evidence samples, implying Gerdes' contamination findings cannot apply to the actual case.

strategic

George Clarke•Dr. John Gerdes

Clarke gets Gerdes to confirm that many 'contaminant' notations were based on very faint, hard-to-see dots that Gerdes reviewed on faded strips — after the original analyst had already seen them at higher intensity.

methodical

Credibility Attacks (2)

⚔ Dr. John Gerdes

methodological limitation / scope challenge

Clarke establishes that Gerdes reviewed fewer than 100 casework samples (less than 10%) and cannot conclude contamination from any evidence sample because he lacks knowledge of the sample's origin and collection conditions — directly undercutting the applicability of his LAPD lab critique to the Simpson evidence.

⚔ Dr. John Gerdes

reliability of observations

Clarke draws out that Gerdes' contamination notations were often based on very faint dots reviewed on faded strips, and that Gerdes was at a 'disadvantage' compared to the original analyst who saw the strips at full intensity.

Witness Demeanor

(Brief pause.)

Objections

None recorded

Proceeding 7184 • 34 utterances • Defense witness

Criminal Trial

Department 103