Redirect examination of William Shields

📄 Redirect examination of William Shields — Thursday, June 22, 1995

Address:

C:\DEPT103\CRIMINAL\1995\JUN\22\REDIRECT-EXAMINATION-OF-WILLIA.DOC

TRIAL

▲ Day 101 of 167

◀ Cross-examination of William Shields (part 2) Recross-examination of William Shields ▶

Witness: Dr. William Shields
Examiner: William Thompson
Called by: Defense • Date: Thursday, June 22, 1995 • Lines: 48

On redirect, defense examiner Thompson has DNA expert Dr. William Shields reassert his qualifications against Dr. Weir (whose party affiliation is unresolved in this packet) and reaffirm his core criticism: Weir's statistical assumptions about mixed bloodstains (items 78/79) lack adequate scientific foundation. Shields distinguishes a Minnesota matter, about which he did not know why the statistics were withdrawn, from a northern California matter involving defendants Heronus and Burch where mixture statistics were withdrawn after the defense prepared to challenge them, and closes by confirming Clarke's cross-examination didn't change his opinion.

# 1 MR. THOMPSON:

Just a few, your Honor.

REDIRECT EXAMINATION BY MR. THOMPSON

# 2 MR. THOMPSON:

Okay. Dr. Weir--excuse me. Dr. Shields, you were asked about your qualifications relative to Dr. Weir's in various areas. Which of the two of you is more qualified in the area of molecular biology?

# 3 DR. SHIELDS:

I am.

# 4 MR. THOMPSON:

Okay. And which of the two of you do you think is more qualified with regard to drawing logical inferences from data produced by molecular biological techniques?

# 5 DR. SHIELDS:

I think we're probably about equally qualified. I know he's convinced me of some things. I think we've come to the same conclusions a number of times.

# 6 MR. THOMPSON:

Okay. Now, Mr. Clarke asked you a number of questions about the assumption regarding the number of contributors that's part of Dr. Weir's computations. Does Dr. Weir also make additional assumptions concerning things like whether alleles are observed and not observed in the stain?

# 7 DR. SHIELDS:

Not in 29, but in 78, yes.

# 8 MR. THOMPSON:

Okay. And so is that an additional assumption that is important in how Dr. Weir computes those numbers?

# 9 DR. SHIELDS:

Yes. It's absolutely necessary.

# 10 MR. THOMPSON:

Okay. And are you con--do you think that there's an adequate scientific foundation for the assumptions that Dr. Weir was making with regard to item 79 or 78?

# 11 DR. SHIELDS:

No, I don't.

# 12 MR. THOMPSON:

Okay. Now--

# 13 DR. SHIELDS:

I do--well--

# 14 MR. THOMPSON:

Please continue.

# 15 DR. SHIELDS:

On item 78, there's a good match between one of the victims and that stain, and I believe that that's good information. I think that Cellmark declared that inconclusive, and most people, when there's an inconclusive, don't try to do statistics on what's left.

# 16 MR. THOMPSON:

Okay. So do you think that the kind of statistical conclusions that Dr. Weir computed in connection with item 78 are scientifically valid?

# 17 DR. SHIELDS:

Valid is an interesting term when you're talking about this sort of thing. It follows from his assumptions.

# 18 MR. THOMPSON:

Yeah. Let me ask--

# 19 DR. SHIELDS:

I don't think it's appropriate.

# 20 MR. THOMPSON:

All right. That was my next question. So you think it's inappropriate?

# 21 DR. SHIELDS:

It is valid, but inappropriate.

KEY QUOTE

# 22 MR. THOMPSON:

Okay. Now, I wanted to ask you a little bit more about this case you mentioned in Minnesota where statistics were offered in connection with mixtures and then withdrawn. Can you tell us why the statistics were withdrawn, if you know?

# 23 DR. SHIELDS:

I don't know for sure.

# 24 MR. THOMPSON:

Okay. Now, do you know of any other case where statistics were offered in connection with mixtures and then later withdrawn?

# 25 DR. SHIELDS:

Yes.

# 26 MR. CLARKE:

Objection. Irrelevant.

# 27 THE COURT:

Overruled.

# 28 MR. THOMPSON:

Okay. Can you tell us about that?

# 29 DR. SHIELDS:

That case was a case in northern California, the Defendants' names were Heronus and Burch, and they were mixtures in which people were attempting to develop frequencies based on the assumption that you would know which of four bands came from which of two defendants without any evidence to back up that you could know that. And under those circumstances, there were discussions about how one should handle that, and in essence, it ended up being withdrawn.

KEY QUOTE

# 30 MR. THOMPSON:

Was this a case in which the Defense was preparing to challenge those kinds of statistical computations?

# 31 DR. SHIELDS:

Yes.

# 32 MR. THOMPSON:

And was the evidence drawn after it became apparent to the Prosecution such a challenge was forthcoming?

# 33 DR. SHIELDS:

On the basis of a letter from the Prosecutor in that case, yes.

# 34 MR. THOMPSON:

Okay. Which laboratory was involved in this case in Minnesota?

# 35 DR. SHIELDS:

The FBI.

# 36 MR. THOMPSON:

Okay. Does the--in the FBI's protocol, is there a section that describes how--

# 37 DR. SHIELDS:

It was the FBI's database. It was Minnesota.

# 38 MR. THOMPSON:

Okay. So it was the Minnesota lab--

# 39 DR. SHIELDS:

Bureau of Criminal Apprehension.

# 40 MR. THOMPSON:

Are you aware of any forensic laboratories that as part of their protocol have a discussion of how to compute statistics in the case of mixtures?

# 41 DR. SHIELDS:

No.

# 42 MR. THOMPSON:

Okay. What--to--in your understanding, what do labs generally do when confronted with a--say a mixed bloodstain?

# 43 DR. SHIELDS:

I can only base it on the three cases of where I've seen that, four cases. And what they will do is, they will end up providing a statistic that's associated with--they will say that someone's not excluded and they will provide then the frequency of the pattern that is the person who is not excluded's rather than the frequency of the individuals who would not be excluded.

# 44 MR. THOMPSON:

Okay. One moment, your Honor.

# 45 MR. THOMPSON:

Dr. Shields, have you changed your mind about the appropriateness of Dr. Weir's calculations as a result of any other questions Mr. Clarke has asked you?

# 46 DR. SHIELDS:

No.

# 47 MR. THOMPSON:

Okay. Thank you.

# 48 MR. THOMPSON:

No further questions.

Temperature

procedural

Key Quotes (4)

Dr. William Shields

It is valid, but inappropriate.

Crystallizes the defense's core DNA critique — Weir's math follows logically from his assumptions but the underlying application is scientifically unsound.

Dr. William Shields

I am.

Directly asserts superior qualification over Dr. Weir in molecular biology, undercutting Dr. Weir's credibility.

Dr. William Shields

No, I don't.

Flat rebuttal of whether Weir's item 78/79 assumptions had adequate scientific foundation.

Dr. William Shields

That case was a case in northern California, the Defendants' names were Heronus and Burch, and they were mixtures in which people were attempting to develop frequencies based on the assumption that you would know which of four bands came from which of two defendants without any evidence to back up that you could know that.

Shows Shields describing a northern California case in which mixture statistics were withdrawn after the defense prepared to challenge them, supporting the defense's critique of Weir's calculations.

Evidence (2)

Item 78

A bloodstain sample that Shields testified showed a good match with one of the victims and that he thought Cellmark had declared inconclusive; Dr. Weir nonetheless computed mixture statistics on it.

challenged

Item 79

A DNA item (RFLP classification unresolved) referenced alongside item 78 as one where Dr. Weir's contributor-number and allele assumptions were applied.

discussed

Notable Exchanges (2)

William Thompson•Dr. William Shields

Thompson walks Shields through why Dr. Weir's statistical conclusions on item 78 are 'valid' in a narrow mathematical sense but scientifically 'inappropriate' given Shields's belief that Cellmark had called the sample inconclusive.

strategic

William Thompson•Dr. William Shields

Shields recounts the northern California Heronus/Burch case where mixture statistics were withdrawn once the defense signaled a challenge, drawing a direct parallel to the current case.

revealing

Credibility Attacks (1)

⚔ Dr. Weir

methodology challenge

Shields testifies that Weir's statistical assumptions about contributor counts and allele presence/absence in items 78/79 lack adequate scientific foundation, and that his item 78 calculation, while internally valid, was an inappropriate use of data Shields thought Cellmark had declared inconclusive.

Objections

1 objections (0 sustained, 1 overruled)

Proceeding 6518 • 48 lines • Defense witness

Criminal Trial

Department 103