Cross-examination of Dr. Robin Cotton (part 1)

📄 Cross-examination of Dr. Robin Cotton (part 1) — Monday, May 15, 1995

Address:

C:\DEPT103\CRIMINAL\1995\MAY\15\CROSS-EXAMINATION-OF-DR-ROBIN-.DOC

TRIAL

▲ Day 74 of 167

Witness: Dr. Robin Cotton
Examiner: Peter Neufeld
Called by: Prosecution • Date: Monday, May 15, 1995 • Utterances: 31

Peter Neufeld resumes cross-examination of DNA expert Dr. Robin Cotton, picking up from Friday's session on item 29 — a mixed bloodstain on the steering wheel. Neufeld methodically extracts admissions that the DNA mixture analysis cannot determine whether two, three, four, or more people contributed to the sample. The examination ends mid-exchange as Neufeld moves to have Cotton physically add a 'third person' card to the prosecution's board, underscoring the unknown-contributor problem.

# 1 MR. NEUFELD:

Good morning, Dr. Cotton.

# 2 DR. COTTON:

Good morning, Mr. Neufeld.

# 3 MR. NEUFELD:

What I would like to do, Dr. Cotton, is return to item 29 very briefly, which is where we left off Friday. On direct examination you had testified that the Prosecutor's board was not correct because it failed to include Nicole Brown Simpson as a potential contributor to the mixed bloodstain on the steering wheel; is that correct?

# 4 DR. COTTON:

That's correct.

# 5 MR. NEUFELD:

And that is why you wrote in the name "Brown"?

# 6 DR. COTTON:

Yes.

# 7 THE COURT:

All right. We need to prop that up so the jury can see what we are talking about here.

# 8 MR. NEUFELD:

Yes.

# 9 (Brief pause.)

# 10 MR. NEUFELD:

Thank you.

# 11 MR. NEUFELD:

And Dr. Cotton, on Friday during cross-examination you admitted that the no. 4 allele reflects the presence of a potential third person into that mixture; is that correct?

# 12 MR. CLARKE:

Objection, vague.

# 13 THE COURT:

Overruled.

# 14 DR. COTTON:

The 4 allele, if you assume that there are three people, the 4 allele is a third person. Alternatively, the 4 allele could just be a second person.

KEY QUOTE

# 15 MR. NEUFELD:

Well, isn't that true in fact with--

# 16 DR. COTTON:

You do--

# 17 MR. NEUFELD:

I'm sorry.

# 18 DR. COTTON:

You can't tell from this data whether there is two or three people there.

KEY QUOTE

# 19 MR. NEUFELD:

In fact, in any instance where you have more than two alleles, let's say you have three or four alleles present, you can't tell whether it is a mixture of two people or more than two people, correct?

# 20 DR. COTTON:

That's right.

# 21 MR. NEUFELD:

It could be three people, right?

KEY QUOTE

# 22 DR. COTTON:

Could be.

# 23 MR. NEUFELD:

It could be four people?

# 24 DR. COTTON:

It could be.

# 25 MR. NEUFELD:

Right. But if we are now simply referring to the column on that board, the second to the last column that says "not excluded," you would agree, I think you have already said, that Mr. Simpson cannot be excluded, correct?

# 26 DR. COTTON:

That's right.

# 27 MR. NEUFELD:

And I think you also said that you would agree that Nicole Brown Simpson cannot be excluded as well, correct?

# 28 DR. COTTON:

That's right.

# 29 MR. NEUFELD:

But you are also saying that you can't exclude some other person whose identity is unknown; isn't that correct, who possesses that 4 allele?

# 30 DR. COTTON:

That's right.

# 31 MR. NEUFELD:

So what I would like you to do, Dr. Cotton, is to add, if you would, under the category that says "not excluded," this additional card that says "third person"--

Temperature

procedural

Key Quotes (3)

Dr. Robin Cotton

You can't tell from this data whether there is two or three people there.

Core concession that mixture interpretation is fundamentally ambiguous — the foundation of Neufeld's third-person argument.

Peter Neufeld

It could be three people, right? ... It could be four people?

Neufeld pushes Cotton to acknowledge the ambiguity is open-ended, not capped at three contributors.

Dr. Robin Cotton

The 4 allele, if you assume that there are three people, the 4 allele is a third person. Alternatively, the 4 allele could just be a second person.

Cotton resists a clean concession, clarifying the interpretive branching — but Neufeld uses both branches to his advantage.

Evidence (2)

Informal

Prosecution's DNA board — a visual chart showing 'not excluded' contributors to the mixed bloodstain on the steering wheel (item 29)

discussed and challenged; Neufeld attempts to have Cotton add a 'third person' card to the board

Informal

Item 29 — mixed bloodstain on the steering wheel, analyzed for multiple potential contributors including OJ Simpson and Nicole Brown Simpson

discussed

Notable Exchanges (1)

Peter Neufeld•Dr. Robin Cotton

Neufeld walks Cotton through the logical chain: more than two alleles present → can't determine two vs. three vs. four contributors → therefore an unknown third person cannot be excluded. Cotton agrees at each step, giving Neufeld the building blocks for the 'third person' card demonstration.

strategic

Credibility Attacks (1)

⚔ prosecution's DNA board

demonstrative evidence challenge

Neufeld targets the prosecution's visual exhibit for omitting Nicole Brown Simpson as a contributor and for not reflecting the ambiguity of a potential unknown third contributor — forcing Cotton to physically annotate the board to correct it.

Witness Demeanor

(Brief pause.) — after board is repositioned for jury visibility

Objections

1 objections (0 sustained, 1 overruled)

Proceeding 6054 • 31 utterances • Prosecution witness

Criminal Trial

Department 103