Recross-examination of Dr. Robin Cotton

📄 Recross-examination of Dr. Robin Cotton — Wednesday, May 10, 1995

Address:

C:\DEPT103\CRIMINAL\1995\MAY\10\RECROSS-EXAMINATION-OF-DR-ROBI.DOC

TRIAL

▲ Day 71 of 167

◀ Redirect examination of Dr. Robin Cotton Motion: DNA mixture analysis ▶

Witness: Dr. Robin Cotton
Examiner: Peter Neufeld
Called by: Prosecution • Date: Wednesday, May 10, 1995 • Utterances: 21

Neufeld conducted a brief recross of DNA expert Dr. Robin Cotton, pressing her on a mathematical argument about genotype frequency calculations for mixed DNA samples — specifically whether excluding impossible genotypes yields a contributor-independent probability figure. Cotton declined to confirm or deny the premise, and Ito shut down Neufeld's attempt to revisit a previously asked question about the NRC report.

# 1 MR. NEUFELD:

Very briefly, your Honor.

# 2 THE COURT:

Briefly.

RECROSS-EXAMINATION BY MR. NEUFELD

# 3 MR. NEUFELD:

First of all, Dr. Cotton, if you have 21 genotypes and you know which alleles are not present, you could take all the possible heterozygous and homozygous type frequencies for those alleles that are not present and add up the sum of those frequencies, could you?

# 4 DR. COTTON:

Yes, the ones that could be present plus the ones that couldn't be present equal the total.

# 5 MR. NEUFELD:

Exactly. So if you start out with a hundred percent and you subtract the genotype frequencies which could not be present--which could not have contributed to that mixture and you subtract that from a hundred percent, you are left with some number, right?

# 6 DR. COTTON:

Yes.

# 7 MR. NEUFELD:

That number is the same whether you have two contributors, three contributors or ten contributors; isn't that right?

# 8 DR. COTTON:

I'm not so sure that that is right.

KEY QUOTE

# 9 MR. NEUFELD:

Are you sure that it is wrong?

KEY QUOTE

# 10 DR. COTTON:

No. Some.

# 11 THE COURT:

That is real helpful.

KEY QUOTE

# 12 DR. COTTON:

These calculations--

# 13 MR. NEUFELD:

Well--

# 14 DR. COTTON:

Sometimes I have to take a piece of paper and work on them and then answer that question. I'm not sure that it is wrong, but I'm not sure that it is right.

KEY QUOTE

# 15 MR. NEUFELD:

Okay. And just getting back to one other point, other than the NRC report which says that you indeed have to aggregate this data, you are aware of no authority to the contrary?

# 16 THE COURT:

You have already asked that question.

# 17 MR. NEUFELD:

Okay. The only point I would make, your Honor--

# 18 THE COURT:

We are not in argument yet.

# 19 MR. NEUFELD:

All right.

# 20 THE COURT:

Anything else?

# 21 MR. NEUFELD:

No.

Temperature

procedural

Key Quotes (4)

Dr. Robin Cotton

I'm not so sure that that is right.

Cotton declines to validate Neufeld's mathematical framework, undermining the defense's attempt to establish a simpler population statistic.

Peter Neufeld

Are you sure that it is wrong?

Classic impeachment pivot — Neufeld catches Cotton in an uncertain middle ground, neither confirming nor denying his premise.

Lance A. Ito

That is real helpful.

Dry judicial sarcasm at Cotton's equivocal non-answer, one of Ito's rare moments of visible irritation.

Dr. Robin Cotton

Sometimes I have to take a piece of paper and work on them and then answer that question. I'm not sure that it is wrong, but I'm not sure that it is right.

Unusually candid admission of uncertainty from an expert witness on a core statistical question.

Evidence (1)

Informal

NRC report — cited as authority requiring aggregation of DNA frequency data

discussed

Notable Exchanges (2)

Peter Neufeld•Dr. Robin Cotton

Neufeld walked Cotton through a step-by-step mathematical argument that subtracting impossible genotype frequencies from 100% yields a contributor-count-independent number; Cotton refused to agree or disagree, eventually saying she'd need paper to work it out.

strategic

Peter Neufeld•Lance A. Ito

Neufeld tried to revisit the NRC report question and pivot to argument; Ito cut him off twice, noting the question had already been asked and that argument time had not begun.

procedural

Light Moments (1)

Lance A. Ito

Ito's deadpan 'That is real helpful.' in response to Cotton's equivocal non-answer about the math.

Credibility Attacks (1)

⚔ Dr. Robin Cotton

exposing uncertainty

Neufeld maneuvered Cotton into admitting she could neither confirm nor deny his statistical premise, leaving her appearing uncertain on a foundational DNA mixture calculation.

Objections

1 objections (1 sustained, 0 overruled)

Proceeding 5993 • 21 utterances • Prosecution witness

Criminal Trial

Department 103