Monthly Archives: December 2011

Rhode Island arrests man following a partial match

A Rhode Island newspaper reports that “[t]he Cranston Police Department has arrested 49-year-old David Finegan, of no permanent address, for the burglary and sexual assault of an 81-year-old woman.” [1] Police “collected [DNA] at the crime scene on May 2.” On June 10, the Rhode Island Department of Health reported that it had a DNA profile from the crime with which to query an offender database. The Rhode Island laboratory did not use software designed for kinship searching, but on July 8, the department advised detectives that it had found a partial DNA match to a female inmate.

The article does not speculate on why it took a month to complete a routine computer search and report the results.Was it because of legal concerns? Was the partial match trawl intentional, or was the discovery inadvertent? Whichever it was, the detectives turned their attention to five male siblings. They discovered that one of them, David Finegan, was “in close proximity . . . on the night of the incident.”

Why this roundabout method of identifying Finegan? He was on parole in July. Was the underlying offense not one that triggered entry into the DNA database? Was there a backlog in entering offender profiles into the database? Whatever the explanation, Finegan had the misfortune of being picked up on July 14 on a parole violation and held for the weekend. Detectives quickly obtained a search warrant and took a sample of DNA from him before he made bail and dropped out of sight. A week later, they learned that it matched the crime-scene DNA.

Pursuing an anonymous tip, police found and arrested Finegan in Providence. He “is being charged with burglary and first-degree sexual assault.” Interestingly, he has an arrest record (including domestic assault, felony DWI, resisting arrest and other assaults) dating back to 1991. A bill that would expand the state database to include arrestees is before House and Senate committees in Rhode Island.


1. Joe Kernan, Arrest Made in Rape of Elderly Woman, Cranston Herald, Dec. 19, 2011


Thanks to Frederick Bieber for informing me of the Cranston Herald article.

Williams v. Illinois (Part II: More Facts, from Outside the Record)

This morning, Professor Richard Friedman posted a revealing report that Cellmark sent to the Illinois State Police (ISP) in Williams v. Illinois. As he explains, and as my previous posting on the facts of the case indicated, the report consists of much more than “machine-generated” statements. But the report — which is a “lodging” that is not part of the record in the case — and Professor Friedman’s remarks warrant a revision to my presentation of the facts of the case and some queries about the ethics of the state’s presentation of the DNA evidence.

On cross-examination, ISP analyst Karen Kooi Abbinanti, who examined the blood sample that Williams gave under court order in another case, testified to William’s STR profile. Because ISP analyst Sandra Lambatos, who provided the state’s only evidence of a DNA match, testified that “there [was] 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,” I presumed that the Cellmark report listed this profile as coming from the male fraction of DNA in the vaginal swab. Indeed, Lambatos testified that the “allele chart” in the Cellmark report “included data that [she] used to run [her] data bank search.” Joint Appendix at 61. Thus, I wrote that

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 . . . .

Now that the report is lodged, it is clear that this singular profile is not what the anonymous Cellmark analyst and Cellmark’s two laboratory directors, Robin Cotton and Jennifer Reynolds, signed off on. Their table, which was Lambatos’s “data,” has the entry of (10, 12, 13) instead of (12, 13) for the D5S818 locus. Had Ms. Lambatos used this tri-allelic genotype, Williams would have been excluded! (Tri-allelic, single locus profiles are rare, but they are not unheard of. For example, one paper reports three cases of tri-allelic patterns observed during routine forensic casework on 5964 Belgian residents [1], and the D5S818 (10, 12, 13) profile has been observed [2].)

Ms. Lambatos, however, testified on cross-examination that the Cellmark report’s “deduced male donor profile” (to quote the report itself) was not actually a deduced profile, but only a list of deduced alleles. Joint Appendix at 71. Interpreting it in this fashion (which may well be the correct understanding what the unknown analyst meant to write), she searched the unspecified database for certain two-allele subsets of the three alleles– namely, (13, 13), (10, 13), and (12, 13). Id. This made sense because, if Cellmark had correctly identified the victim’s profile — something that Lambatos did not check — then the rapist rather than the victim had to be the source of the 13-repeat allele.

The circumscribed nature of Ms. Lambatos’s testimony on direct examination about the “DNA match” is worthy of comment. Full disclosure would have required a scientist to reveal that other male profiles than just Williams’ profile were “consistent with” the vaginal-swab mixture and could have been picked out of a database in her trawl. Instead, Ms. Lambatos acquiesced in or suggested confining her testimony to Williams’ matching profile and the random-match probability associated with that one profile. In other words, she chose not to acknowledge possibilities that were inconsistent with the state’s theory. Does such selectivity contravene the professional responsibility of forensic scientists to “[a]ttempt to qualify their responses while testifying when asked a question with the requirement that a simple ‘yes’ or ‘no’ answer be given, if answering ‘yes’ or ‘no’ would be misleading to the judge or the jury”? [1]

The answer, I think, depends on how misleading Ms. Labatos’s answers on direct examination were. This was not a case of a single profile that probably could exclude everybody except a twin brother. The analysts were unable to distinguish between Sandy Williams and other males with similar, but not identical profiles, as possible sources of the male DNA. By not disclosing this fact, Ms. Lambatos and the prosecutor made the DNA “match” sound especially compelling. The prosecutor asked about “the male DNA profile found in the semen.” Ms. Labatos made no effort to correct or clarify even though she firmly believed that Cellmark was reporting at least three different male profiles for the semen (and that Williams was, of course, a match to only one of them). Hammered with Ms. Lambatos’s figures for the Williams’ profile frequency, a judge surely would think that only Williams could have been the rapist. In contrast, a judge who understood that Cellmark’s tests pointed to men with other DNA profiles might have been more willing to entertain some doubt.

The counterargument is that the probative value of the evidence for the ambiguous profile is essentially the same as the probative value of the evidence for the unambiguous profile that Ms. Lambatos was asked about. There probably are no other men in Chicago with the alternative profiles. Assuming that the vaginal swab DNA is a mixture of the victim’s DNA and one man’s DNA, and assuming that the laboratory called all the alleles correctly, the likelihood ratio for the hypotheses of Williams versus that of a random, unrelated man is 1/[p(10,12,13) + p(13,13) + p(10,13) + p(12,13)], where p is the random-match probability for the full genotype, including the alleles shown in parentheses. Ms. Lambatos computed the probability p(12,13) as falling in the quadrillionths. Although I have not consulted allele frequency tables, it is a safe bet that similarly small probabilities would pertain to the profiles with the (13,13) and (10,13) genotypes. The random-match probability for the profile with the tri-allelic pattern would be even smaller. (When asked by the defense, Ms. Lambatos testified that a tri-allelic male was not a real possibility.) Therefore, I would predict that the correct computation would differ from the number given to the judge by less than an order of magnitude. Hence, the witness’s failure to clarify or correct the prosecutor in her questioning affected the probative value of the evidence minimally.

Nevertheless, for the expert to present such oversimplified testimony without any qualification seems problematic to me. When confronted with the omissions on cross-examination, the expert owned up to them, but did she ask the prosecutor to present the expert’s reasoning accurately in the first place? And if she did ask, why didn’t the prosecutor do it?


1. G. Mertensemail, S. Rand, E. Jehaes et al., Observation of Tri-allelic Patterns in Autosomal STRs During Routine Casework, 2 Forensic Sci. Int’l: Genetics Supplement Series 38-40 (2009).

2. NIST STR-base, Tri-Allelic Patterns, June 2, 2011,

3. American Society of Crime Laboratory Directors Laboratory Accreditation Board, ASCLD/LAB Guiding Principles of Professional Responsibility for Crime Laboratories and Forensic Scientists, Principle 19, Version 1.1, 2009.

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 these opinions? 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 outline what I was able to extract by reading the trial transcript about the “data” (as the witness called it) used in forming her “independent, expert opinions” (as Illinois characterizes 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 as follows:

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 contain epithelial cells from the victim and varying numbers of sperm cells. The former cells lead to a female fraction of DNA, the ones latter to a male fraction. The profiles from each individual’s DNA 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 extracting the female DNA first, and then extracting the male DNA. The latter extract, ideally, 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 (from the victim’s reference blood sample) and attributing the remainder to the rapist. This was not as simple as it sounds, because the 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 a mixture electropherogram.

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.

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 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 STR profile of Williams’ reference blood sample (analyzed by Kooi) matched the 13 pairs that constituted the male fraction in the vaginal swab (according to Cellmark’s report).

At some point before the trial, Lambatos looked at one of the electropherograms from Cellmark — the one for the mixture extracted from 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 profile as a given and looked only at the mixture electropherogram to infer the rapist’s DNA 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 simple 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.

Update on Pennsylvania Senate Bill 775

By a vote of 42-6, the Pennsylvania Senate passed a bill (discussed here on March 18, 2011) to begin taking DNA samples on arrest and to authorize kinship trawling in some cases. The proposed changes come with a price tag. Although the state police laboratory is reducing the backlog of convicted-offender samples, it hardly has surplus capacity. The appropriations committee’s fiscal note estimates the cost for laboratory staff and supplies for phasing in just a portion of the samples that could be collected from arrested at more than $560,000 in 2012-13.