Wednesday, December 14, 2011

Williams v. Illinois (Part I: Just the Facts)

The Supreme Court heard oral argument last week in Williams v. Illinois. The case could have been just another of the thousands of rape cases that work their way through state courts across the country. But the prosecution decided to take a shortcut to convict Sandy Williams. Rather than present the laboratory analyst who produced the DNA profiles of the victim and the rapist, it had an analyst from a completely different laboratory testify in a bench trial. This gap in the state's case eventually attracted the attention of the U.S. Supreme Court. Indeed, Williams is the third case in as many years in which the Supreme Court has agreed to review criminal convictions relying on the findings of laboratory workers who do not appear at trial.

Unsurprisingly, the parties frame the issue before the Court differently. On one hand, according to Williams the question is
Whether the prosecution violates the Confrontation Clause when it presents . . . the substance of a testimonial forensic laboratory report through the trial testimony of an expert witness who took no part in the reported forensic analysis, where the defendant had no opportunity to confront the analysts who authored the report.
Brief for Petitioner at i. On the other hand, according to the state, the issue is
Whether a criminal defendant’s Sixth Amendment right to confront witnesses against him is satisfied where a prosecution expert testifies live at trial to her independent, expert opinions and is subject to unrestricted cross-examination.
Brief for Respondent at i.

How can the expert’s opinions be “independent” if she simply took what someone else told her as true in forming them? What is the value of “unrestricted cross-examination” when the witness’s knowledge of what transpired is so severely restricted? Understanding what information the testifying witness relied on seems crucial to an informed resolution of the case. Yet, the prosecution elicited no detailed information on this at trial. In this posting, I shall describe the facts of the case more fully and what I was able to extract by reading the trial transcript about the “data” (as the state’s witness called it), used in forming her “independent, expert opinions” (as Illinois calls them). Later postings will comment on the oral argument and the legal issues.

The Rape Kit

The Supreme Court of Illinois outlined the events leading to the submission of biological evidence to the state laboratory:
On February 10, 2000, 22–year–old L.J. worked until 8 p.m. as a cashier at a clothing store in Chicago. On her way home . . . [a]s she passed an alley, the defendant came up behind her and forced her to sit in the backseat of a beige station wagon, where he [sexually assaulted her]. He then pushed L.J. out of the car while keeping L.J.'s coat, money, and other items. After L.J. ran home, her mother opened the door and saw her in tears, partially clothed with only one pant leg on. [H]er mother called the police.

Shortly after 9 p.m., Chicago police officers arrived at the home . . . . After L.J. told the officers what had transpired, the officers issued a “flash” message for a black male, 5 foot, 8 inches tall, wearing a black skull cap, a black jacket and driving a beige station wagon. An ambulance transported L.J. and her mother to the emergency room. [V]aginal swabs . . . were . . . placed into a criminal sexual assault evidence collection kit along with L.J.'s blood sample. The kit was sent to the Illinois State Police (ISP) Crime Lab for testing and analysis.
On February 15, 2000, [a] forensic biologist . . . performed tests that confirmed the presence of semen. . . .
People v. Williams, 939 N.E.2d 268, 270–71 (Ill. 2010).

To Maryland and Back

Like too many police laboratories, the ISP lab was behind in processing rape kits and other DNA samples. So after letting the rape kit sit for nine months, it sent the vaginal swab that it knew contained semen along with the reference sample of LJ’s blood to a private company, Cellmark Diagnostics, in Germantown, Maryland, via Federal Express. Cellmark received the samples the next day (November 29, 2000). Another fours months went by before Cellmark returned the samples and supplied a report (on April 3, 2001).

The analysis of the reference sample of the victim’s blood at Cellmark should have been straightforward. That sample had plenty of DNA purely from LJ. Nevertheless, no one testified about the electropherogram. Was it clean, with clear peaks, or did it have blobs, pull-up, or off-ladder peaks? The transcript of the testimony, reproduced in relevant parts at the end of this posting, does not contain such questions. The testifying expert never looked at this electropherogram or the data underlying it.

The transcript does suggest, however, that the vaginal swab was not so easily analyzed. Vaginal swabs from rape victims often contain epithelial cells from the victim and some number of sperm cells. Extracting the DNA yields a female fraction from the victim’s epithelial cells and a male fraction from the sperm cells. The two DNA profiles will be mixed together, and someone must deduce which male profiles are consistent with the mixture (and the probability that each such profile is present in the mixture).

Sometimes this “mixture deconvolution” can be avoided by a procedure that extracts the female DNA first and then extracts the male DNA (because sperm cells are harder to break open than are epithelial cells). Under ideal conditions, the latter extract contains DNA from the semen cells only. Unfortunately, the differential extraction failed. The second extract still was a mixture of DNA from LJ and the unknown rapist.

So the Cellmark analyst did his or her best to decipher it by “subtracting” the victim’s peaks (as ascertained from the victim’s reference blood sample) and attributing the remaining peaks to the rapist. This was not as simple as it sounds, because the individual STR alleles are not that uncommon, and the victim and the rapist probably had some alleles in common. In any event, the Cellmark analyst arrived at a single profile — a set of 13 pairs of numbers characterizing the DNA that the rapist inherited from his mother and father. The unnamed analyst believed that the semen had the following profile: D3 (16, 19), DWA (17, 17), FGA (18.2, 22), D8 (14, 14), D21 (29, 30), D18 (13, 17), D5 (12, 13), D13 (11, 11), D7 (10, 12), D16 (9, 11), TH01 (7, 7), TPOX (11, 11), and CSF (8, 10). The analyst’s report included this profile and LJ’s profile (derived from her reference blood sample) as well as at one electropherogram from the mixture.

Meanwhile Williams’ Profile Goes Into the Police Database

During this year of desultory activity, Sandy Williams ran into trouble with the Chicago police:
On August 3, 2000, police arrested the defendant for an unrelated offense and, pursuant to a court order, drew a blood sample from [him]. On August 24, 2000, forensic scientist Karen Kooi [at the ISP lab] performed an analysis on the sample . . . . Kooi extracted a [DNA] profile and entered it into the database at the ISP Crime Lab.
Williams, 939 N.E.2d at 270–71. Which database this was is not clear. It seems unlikely that it was the state’s database for linking known criminals to crime-scene samples, for that database was limited to convicted offenders. Only this year did Illinois pass a law to extend the state database to include certain arrestees.

ISP Uses the Cellmark Profile to Pick Out Williams

The analyst at the police lab who received the materials from Cellmark was Sandra Lambatos. Her testimony is rather fuzzy with regard to how she proceeded. I cannot tell for certain whether she immediately entered the male profile as Cellmark reported it into the unspecified computer database system or whether she waited to do that until she looked more deeply into Cellmark’s report. In any event, the queried the database for the profile that Cellmark reported must have come from the sperm. Bingo! This profile matched the profile of Williams taken after his arrest in August. Every 13-locus profile is exceedingly rare in the general population — perhaps unique to an individual and any identical twins.

Police put Williams in a line-up on April 17, 2001, and LJ identified him as the man who sexually assaulted her over a year earlier.

The ISP Analyst Testifies — and the Cellmark Analyst Does Not

At trial, the state did not call anyone from Cellmark — the laboratory that did the DNA profiling of the vaginal swab. It relied instead on Ms. Lambatos to talk about the results. Lambatos verified that the 13 pairs of numbers that constituted the ISP’s profile of Williams’ reference blood sample were the same as the 13 pairs that constituted the male fraction reported by Cellmark. This established that the database profile with Williams’ name associated with it was, indeed, Sandy Williams’ profile.

At some point before the trial, Lambatos looked at one of the electropherograms from Cellmark — the one following the differential extraction for the mixture in the vaginal sample. She did not take the Cellmark electropherograms from the victim and from the vaginal swab mixture and compare them herself to deduce the rapist profile. Instead, she accepted Cellmark’s report of the victim’s profile as a given and looked only at the mixture electropherogram to infer the rapist profile.

In short, from what I can glean from the testimony, Cellmark's deduction of the male profile is a nontrivial, human inference (although it also could be done with software). But it also looks as if Lambatos made the same deduction using (1) Cellmark's electropherogram of the mixture, and (2) the alleles reported by Cellmark for the reference sample of the victim's blood. With regard to the alleles in (2), getting from the electropherogram for the victim's reference sample of blood to her STR profile could have been quite simple, but there could have been a bit of interpretation there too. In any event, this is not a case of an interpretive analyst starting with two electropherograms of single-source profiles — Lambatos' testimony about forming an "independent opinion" from the Cellmark "data" notwithstanding.

Excerpts from the trial testimony of Sandra Lambatos
identifying Sandy Williams as the rapist

Direct examination [JA 42]

Q  What is your current occupation?
A  I am a stay-at-home mom. [JA 43]
Q  Where did you work before that?
A  At the Illinois state police crime laboratory.
. . . [JA 51]
Q  [O]n the date of November 28th of 2000, was evidence from this case sent to (Cellmark) diagnostic laboratory . . . ?
. . . [JA 52]
Q  What was the evidence that was sent?
A  Vaginal swab and a blood standard from [LJ].
. . . [JA 54]
Q  And does this [shipping manifest] indicate the date that the evidence . . . was sent back . . . from (Cellmark) . . . ?
A  It does.
Q  And what is the date . . . ?
A  April 3d of 2001.
. . . [JA 56]
Q  Was there a computer match generated of the male DNA profile found in semen from the vaginal swabs of [LJ] to a male DNA profile that had been identified as having originated from Sandy Williams?
A  Yes, there was.
Q  Did you compare the semen . . . from the vaginal swabs . . . to the male DNA profile that had been identified by Karen Kooi from the blood of Sandy Williams? [JA 57 ]
A  Yes, I did.
. . .
Q  What was your conclusion?
A  I concluded that Sandy Williams cannot be excluded as a possible source of the semen identified in the vaginal swabs.
Q  In other words, is the semen identified in the vaginal swabs of [LJ] consistent with having originated from Sandy Williams?
A  Yes.
Q  What is probability of this profile occurring in the general population?
. . .
A  This profile would be expected to occur in approximately 1 in 8.7 quadrillion black, 1 in 390 quadrillion white, or 1 in 109 quadrillion Hispanic unrelated individuals.
. . . [JA 58]
Q  In your expert opinion, can you call this a match to Sandy Williams?
A  Yes.

Cross examination [JA 61]

Q  And that report [from Cellmark dated Feb. 15, 2001] included an allele chart, correct?
A  Yes.
. . .
Q  And that included data that you used to run your data bank search.
A  Correct. [JA 62]
Q  You did not interpret the results by [Cellmark], did you?
A  Partially. I did review their data, and I did make my own interpretations. So I looked at what the programs, what they sent to me, and did make my own interpretation, my own opinion.
Q  That would be the vaginal swab with respect to the electropherogram E2, right?
. . .
A  Yes.
Q  You did not receive electropherograms for the E1?
A  I believe all I have in my case file is E2, correct.
Q  And you did not receive electropherograms from the standard of [LJ], did you?
A  No, I did not.
. . . [JA 68]
Q  And you reviewed the electropherograms just for that second fraction from the differential extraction [procedure], correct?
A  Correct.
Q  You did not receive the electropherograms for the first part of the procedure, that first part of the extraction, did you?
A  Correct.
. . . [JA 69]
"[T]hey sent the chart that was in the F1 fraction E1. Also the profile that was in the E2 fraction and the profile that was in [LJ]'s standard, and I had only the electropherograms from the E2 fraction . . . .
Q  But you did not receive their data or their electropherograms?
A.  No, I did not receive electropherograms for those fractions.
Q  You never received any computer data, the electronic data.
A   I myself did not receive that, but that was sent to the laboratory.
Q  You never viewed that?
A  Oh no, I did not.

First posted to The Double Helix Blog, 13 Dec. 2011

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