Williams v. Illinois (Part II: More Facts, from Outside the Record, and a Question of Ethics)

This morning, Professor Richard Friedman posted a revealing report that Cellmark sent to the Illinois State Police (ISP). As he explains, and as my previous posting on the facts of Williams v. Illinois indicated, the report consists of much more than "machine-generated" statements. But the "lodging" (not part of the record in the case) and Professor Friedman’s remarks warrant a few additions or revisions to my presentation of the facts of the case.

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’s 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 for 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 or a mythical twin could have been the rapist. In contrast, a judge who understood that Cellmark's tests also 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. 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 not differ from the number given to the judge by more than an order of magnitude. Hence, the witness’ 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 not ask the prosecutor to present the expert's reasoning accurately in the first place? And if she did, why did the prosecutor not do it?

References

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, http://www.cstl.nist.gov/strbase/var_D5S818.htm#Tri

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.

Cross posted from The Double Helix Law Blog, 15 Dec. 2011

Was the White Powder Cocaine? Apparently so, but Melendez-Diaz Acquitted

In February, the Boston Globe reported the acquittal of Luis Melendez-Diaz [1]. Melendez-Diaz gained legal fame when the Supreme Court reversed his initial conviction for drug trafficking because the Commonwealth of Massachusetts used sworn "certificates of analysis" from a state laboratory to show that a white powder was cocaine. [2] A state statute allowed this official hearsay, and the certificates were not accompanied oral testimony (or even a written report) of how the laboratory reached this conclusion.

On retrial, the Commonwealth "called to the stand a chemist from the state Department of Public Health who testified that the substance allegedly found in the back seat of a police cruiser with Melendez-Diaz and two other men in 2001 had tested positive for cocaine." Apparently the accuracy of the laboratory's finding was not in dispute. The defense lawyer said that the case "really seemed to be about guilt by association." Police had arrested Melendez-Diaz and two other men and placed them in the back of a police cruiser. Because the officers saw the men fidgeting on the way to the police station, they searched the car and found 19 bags of a white substance.

Evidently, Melendez-Diaz's proximity to the bags did not convince the jurors of his guilt. A spokesman for the district attorney's office said that “We’re 10 years out from the original incident, and the passage of so much time only makes a case tougher to try. The acquittal did not free Melendez-Diaz, who is serving a separate 10-year sentence for drug trafficking.

References

1. Martin Finucane, Drug Defendant Retried on High Court’s Order Is Acquitted, Boston Globe, Feb. 11, 2011.

2. Melendez-Diaz v. Massachusetts, 557 U.S. __, 129 S. Ct. 2527 (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 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.

Appendix
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

Legislation to Implement Kinship Matching in Criminal DNA Databases

A few years ago, “Jeffrey Rosen, a constitutional law professor at George Washington University, warned: ‘I can guarantee if familial searching proceeds, it will create a political firestorm.’” (1) But familial searching, as it is tendentiously called, prompted no huge political protests when California, Colorado, New York, and Virginia adopted it administratively. Now, legislative initiatives to implement it in various states (2, 3) and federally (4) have begun. However, the proposed legislation is timid, usually authorizing the practice only in murder and sexual assault cases and only after traditional investigative methods have failed.

References

1. Maura Dolan & Jason Felch, California Takes Lead on DNA Crime-fighting Technique: The State Will Search its Database for Relatives of Unidentified Suspects in Hopes of Developing Leads, Los Angeles Times, Apr. 26, 2008

2. Mike Cook, DNA — It’s All in the Family, Minnesota House of Representatives Session Weekly: News from the House, Apr. 8, 2011

3. Mark Scolforo, DNA Proposal Has Foes: Pa. Bill to Expand its Collection Opposed by the ACLU, Phil. Inquirer, Oct. 2, 2011

4. Press Release, Schiff's Familial DNA Language Passes as Part of Conference Report, Nov. 21, 2011

Cross-posted from The Double Helix Law Blog

New Mexico Supreme Court Proposes Rules on Lab Reports

The New Mexico Supreme Court is soliciting comments on "three representative proposals that have been suggested . . . to address the admission of state laboratory forensic analyses in light of Bullcoming." [1] The state court is referring to the U.S. Supreme Court's somewhat unenlightening opinion in Bullcoming v. New Mexico, 131 S. Ct. 2705 (2011), discussed here some months ago. Inasmuch the the rules are a response to a Confrontation Clause decision that applies only in criminal cases, I shall assume that these rules also would apply solely in criminal cases.

The first proposal covers all "forensic scientific evidence including blood and breath alcohol test reports, controlled substance chemical analysis reports." It orders the parties to confer about stipulating to a waiver of the defendant's right to be presented with a laboratory analyst to cross-examine on the laboratory's findings and of the state's right to present a live witness along with the reports. [1]

Of course, the parties can initiate such such discussions now, and they need not stipulate to anything anyway. The proposed rule states that "The report or print-out ... shall not be admitted at trial without the testimony of necessary witnesses unless the defendant stipulates in writing," but that adds nothing of substance to the status quo (or to the rest of the rule).

But what happens if one or more of the parties do not event want to talk about a stipulation. The rule says that "[i]f either party cannot obtain the opposition’s position regarding a proposed stipulated order, that party may file a motion requesting a hearing to determine the opposition’s position regarding the need for testimony ... ." Maybe the judge can induce the parties to take an irrevocable position well before the trial, as the rule seems to contemplate. This might help the lab schedule its staff time, but is all this judicial rule-making worth the effort to achieve this convenience?

Alternative Rule 2 abolishes the hearsay rule as applied to "a written report of the conduct and results of a chemical analysis of breath or blood for determining blood alcohol concentration." Of course, many jurisdictions have statutes to this effect, and others apply the business records exception to reach the same result. The (new?) hearsay exception makes no difference in New Mexico criminal cases as long as the U.S. Supreme Court adheres to the interpretation of the Confrontation Clause articulated in Crawford v. Washington, 541 U.S. 36 (2004).

Alternative 3 requires the prosecution to serve on the defendant "[a] copy of a report of the methods and findings of any examination conducted by an employee of any governmental laboratory ... no later than ninety (90) days before trial" and to give notice to the defense at the same time if it intends to introduce the report into evidence. If New Mexico prosecutors do not already provide timely disclosure of reports or if this provision requires that more complete reports be prepared than is currently the practice, it would be a significant improvement.

Yet, the rule also imposes a burden on the defense to object in writing before trial. In this regard, it reads as follows: "If the defendant does not file a written objection with the court to the use of the laboratory report and certificate within the time allowed by this subparagraph, then the report and certificate are admissible in evidence."

The thinking seems to be that the defense ordinarily should not have to object before trial. However, if the prosecution affirmatively notifies defense counsel that it does not plan to present a necessary witness, then the defense should be forced to make a pretrial demand for confrontation (or lose that right). The rule would require the defendant to give notice at least 30 days before trial. [3] A dictum in Melendez-Diaz v. Massachusetts, 129 S. Ct. 2527 (2009), approves of such notice-and-demand rules. [4]

Interestingly, none of the proposed rules go so far as to place the burden on the defendant to give notice in all cases in which it learns that a laboratory report exists. The state rules committee's commentary to the first alternative rule states: "This rule applies in lieu of a notice and demand rule, which the committee rejected, and is meant to ensure that the waiver is not made by accident or lack of knowledge. The defendant may waive this right by stipulated order, but the waiver shall be made willingly, knowingly, and intelligently."

Notes

1. Myrna Raeder initiated a discussion of these rules on Roger Park's discussion list for law professors. The rules are available at http://nmsupremecourt.nmcourts.gov/rules/pdfs/proposed_alt._rules_1,_2,_3.pdf

2. The proposed rule states that "[t]he parties shall confer and either party may file a stipulated order to admit a report or print-out of results ... or to limit the witnesses required to appear at trial."

3. This proposed rule include the statement that "[i]f the defendant does not file a written objection with the court to the use of the laboratory report and certificate within the time allowed by this subparagraph, then the report and certificate are admissible in evidence ... ."

4. See http://federalevidence.com/node/1228; http://www.scotusblog.com/case-files/cases/briscoe-v-virginia-2/.

DNA Identification Technology: Fast and Furious

Today’s talks at the International Symposium on Human Identification indicated some directions in which DNA-based identification technology will move in the near future. For example, one company reported a way to type 26 different STRs simultaneously. Is that enough to justify testimony of global individualization (with the exception of identical twins)?

The Departments of Defense, Homeland Security, and Justice are seeking self-contained devices for rapid STR profiling and interpretation, and several companies claim to be on the verge of delivering them. “Rapid” means an hour or so, and the hope is that these microfluidic devices will permit on-the-spot (or at-the-police-station) results for investigations as well as DNA database queries and entries. One company promises a functioning product in April 2012. Another refers to an existing instrument “compact enough to be used in an office setting, airport security area, mobile van, or field-forward military site.”

None of these has been fully validated. The FBI is figuring on widespread implementation at local police stations in 4-7 years, but police in Palm Bay, Florida, have posted videos on YouTube to advertise their success with a microfluidic device in “Operation Rapid Hit.”

Finally, companies are supplying police with phenotype and ancestry data, including probable eye and hair color. For the future, the most impressive -- and disquieting -- approach uses “next-generation sequencing” to extract all the usual STRs, together with phenotypically and medically informative data in one fell swoop.

Indeed, sequencing the oral bacteria that we host is possible. A speaker described one individual whose microbiome included a bacterium used in the industrial production of yogurt and cheese. Just imagine the APB: “The suspect is a white male with brown hair (probability = 0.45) and blue eyes (probability = 0.95) who likes yogurt.”

An Odd Set of Odds in Kinship Matching with DNA Databases

The 22d International Symposium on the Future of Human Identification began yesterday with a set of workshops. One was on "familial searching." The phrase refers to trawling the profiles in a DNA database for certain types of partial matches to a DNA profile from a crime-scene sample.

Partial matches that are useful in generating investigative leads to family members arise much more often when a particular kind of relative (say, a full sibling) is the source of the crime-scene sample than when an individual who is not closely related to the database inhabitant is the source. The ratio of the probability of the partial match under the former condition (a given genetic relationship) to the latter (unrelated individuals) is a likelihood ratio (LR). The LR (or, technically, its logarithm) for siblingship expresses the weight of the evidence in favor of the hypothesis that the source is full sibling as opposed to an unrelated individual.

After explaining the this idea, the first speaker presented the following formula:

"Odds" = LR_autosomal x LR_Y-STR x 1/N         (1)

She attributed this formula to the California state DNA laboratory that does familial searching in that state. In this equation, N is the size of the database, LR_autosomal is the likelihood ratio for the partial match at a set of autosomal STR loci, and LR_Y-STR is the likelihood ratio for the matching Y-STR haplotype.

She described this as a Bayesian computation that could lead to statements in court such as "there is a 98% probability" that the person whose DNA was found at the crime scene is a brother of Joe Smith, a convicted offender whose DNA profile is in a DNA database.

There are three interesting things to note about these suggestions. To begin with, it is not clear why such a statement would be introduced in a trial. By the time the suspect has become a defendant, a new sample of his DNA should have been tested to establish a full match to the crime-scene sample. At that point, why would the judge or jury care whether defendant is related to a database inhabitant. The relevance of the DNA evidence lies in the full match to the crime-scene sample, and the jury need not consider whether the defendant is a relative of someone not involved in the alleged crime. (One might ask whether the trawl through the database somehow degrades the probative value of the full match, but, if anything, it increases it. [1])

The issue could arise, however, if police were to seek a court order or search warrant to collect a DNA sample from the suspect. At that point, they would need to describe the significance of the partial match to the convicted offender.

This possibility brings us to the second noteworthy point about equation (1). The "odds" (or the corresponding probability) are not the way to present the weight of the partial match. Consider the prior probability of a match in a small database, say, of size N=2. Prior to considering the partial match, why would one think that the probability of a database inhabitant being the sibling of the criminal who resides outside the database is 1/N = 1/2? It is quite improbable that the database of two people includes a relative of every criminal who leaves DNA at a crime-scene. The a priori probability for a small database must be closer to 0 than 1/N.

That the prior probability is less than 1/N is a general result. The only exception occurs when it is absolutely certain that a sibling of the perpetrator is in the database. On that assumption, prior odds of 1 to N-1 are not unreasonable. But that assumption is entirely artificial, and to advise a magistrate that the posterior odds have the value computed according to (1) would be to overstate the implications of the partial match.

The third thing to note about dividing by N is that it accomplishes nothing in producing a viable list of partially matching profiles in a DNA database trawl. The straightforward approach is to produce a short list of candidates in the database whose first-degree relatives might be the source of the crime-scene sample. The minimum value of LR_autosomal x LR_Y-STR should be large enough to keep the two conditional error probabilities (including a candidate when there is no relationship, and not including a candidate when there is a relationship) small. This threshold value does not depend on N. (A later speaker made this observation.)

Equation (1), it seems, is useless. Instead, the magistrate should be told the value of the LR and how often such large LRs would occur when a crime-scene sample comes from a relative versus how often it would occur when it comes from an related person.

Reference

1. David H. Kaye, 2009, Rounding Up the Usual Suspects: A Legal and Logical Analysis of DNA Database Trawls, North Carolina Law Review, 87(2), 425-503.