ted by courts in the United States. When 2 profiles are found to “match” in a search of the Federal Bureau of Investigation’s (FBI’s) Combined DNA Index System (CODIS) database using 13 short tandem repeat (STR) loci, the likelihood that the profiles came from different people is extremely small. In other words, assuming the samples were properly collected and analyzed, an observer may state with a high degree of confidence that the two profiles likely came from the same person.

Among existing forensic methods, only nuclear DNA analysis has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between an evidentiary sample and a specific individual or source. Indeed, DNA testing has been used to exonerate persons who were convicted as a result of the misapplication of other forensic science evidence.58 However, this does not mean that DNA evidence is always unassailable in the courtroom. There may be problems in a particular case with how the DNA was collected,59 examined in the laboratory,60 or interpreted, such as when there are mixed samples, limited amounts of DNA, or biases due to the statistical interpretation of data from partial profiles.61

Courts were able to subject DNA evidence to rigorous evaluation

U.S. 1086 (2006); United States v. Shea, 957 F. Supp. 331, 340-41 (D.N.H. 1997), aff’d, 159 F.3d 37 (1st Cir. 1998).


According to The Innocence Project, there have been 220 postconviction DNA exonerations in the United States since 1989. See The Innocence Project, Fact Sheet: Facts on Post-Conviction DNA Exonerations. Available at www.innocenceproject.org/Content/351.php; see also B.L. Garrett. Judging innocence. 108 COLUM. L. REV. 55 (2008) (discussing the results of an empirical study of the types of faulty evidence that was admitted in more than 200 cases for which DNA testing subsequently enabled postconviction exonerations); but see J. Collins and J. Jarvis. 2008. The Wrongful Conviction of Forensic Science. CRIME LAB REPORT. Available at www.crimelabreport.com/library/pdf/wrongful_conviction.pdf (contesting the percentage of exonerated defendants whose convictions allegedly were based on faulty forensic science).


See, e.g., W.C. Thompson. DNA evidence in the O.J. Simpson trial. 67 U. COLO. L. REV. 827 (1996) (detailing the defense counsel’s theory that proper procedures were not followed in the collection or handling of the DNA samples at various points in the murder investigation).


See, e.g., L. Hart. 2003. “DNA Lab’s Woes Cast Doubt on 68 Prison Terms.” Los Angeles Times. March 31, at 19; A. Liptak. 2003. “Houston DNA Review Clears Convicted Rapist, and Ripples in Texas Could Be Vast.” New York Times. March 11, at A14; R. Tanner. 2003. “Crime Labs Stained by a Shadow of a Doubt.” Los Angeles Times. July 13, at 18.


See, e.g., Coy v. Renico, 414 F. Supp. 2d 744, 761-63 (E.D. Mich. 2006) (rejecting habeas petitioner’s claim that he was denied a fair trial because the statistical techniques used to evaluate mixed DNA samples were insufficiently reliable); see also B.S. Weir. 2007. The rarity of DNA profiles. Annals of Applied Statistics 1(2):358-370 (suggesting that wholesale searches of large DNA databases for solving cold cases might yield false positives with some regularity).

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