In the People versus Hillary (NY) there were three challenges to the DNA evidence which was presented by Dr John Buckleton. Each of these are described below with the ruling from the court.
1. The defendant filed a motion that STRmix is not generally accepted in the relevant scientific and legal community (that it does not meet the standards of Frye).
The court found that the STRmix method is generally accepted. Specifically,
“The issues of proper foundation and of the adequacy of laboratory procedures are not before [the Court at a Frye hearing]" (People v. Wesley, supra). To that end, this court notes that the New York State Commission on Forensic Science issued a binding recommendation for use of STRmix in the analysis of DNA profiles upon recommendation from its DNA Subcommittee (Executive Law §995-a;People v. Wakefield, supra at 856 [approval by the Commission constitutes general acceptance]). And STRmix was found by a New York State court after a Frye hearing to be generally accepted in the relevant scientific community (People v. Vincent Bullard-Daniel, supra). Based upon a review of the record, this court finds that STRmix has been developmentally validated and is generally accepted as reliable within the scientific community (id; People v. Muhammad, 141h Cir. Ct., Muskegon Co, Dec. 15,2015).” (emphasis added)
2. The defendant filed a motion to preclude the use of a modified RMP statistic.
The LR reported by Dr Buckleton was 526,000 (HPD LR = 335,000). Dr Buckleton also reported a modified RMP statistic of 39 million for the minor contributor. He candidly stated in his statement that “Although the RMP is a standard and accepted approach in the USA it is thought to overstate the value of the evidence in those cases where drop-out is possible such as this case.”
The Court ruled on the RMP statistic that “while this court finds that it has been generally accepted as reliable within the scientific community under certain circumstances, the results produced in this case are unreliable based upon Dr. Buckleton's testimony that it cannot adequately account for the absence of defendant's alleles in the composite profile,”
3. The defendant challenged the admissibility of the evidence.
In this case the laboratory work was conducted by the New York State Police laboratory (NYSP). The prosecution contracted Dr Buckleton and the ESR laboratory to undertake the interpretation of the evidence. The evidence itself was three replicate amplifications of a two person mixed Identifiler Plus profile collected from the fingernails of the deceased. The mixture proportions were approximately 100:1. The major in this profile corresponded to the deceased. Analysed using the New York State Police laboratory’s validated analytical threshold of 50 rfu, there were eleven alleles corresponding to the defendant across the three replicates and no unexplained alleles.
No internal validation studies have been performed by NYSP for the use of STRmix on casework samples developed at that lab. As a result, reasonable parameters were selected from other laboratories in the US who are using STRmix to interpret Identifiler Plus profiles under the same conditions.
The Court determined that the “lack of internal validation by the New York State Police crime lab, as candidly admitted by Dr. Buckleton, precludes use of the STRmix results”.
Honorable Felix J. Catena, the County Court judge ruled:
"It is, therefore, ORDERED that the defendant's motion to preclude the prosecution from calling an expert witness to testify on their direct case regarding any conclusion reached by the use of STRmix is granted as the prosecution cannot lay a foundation for the introduction of evidence that had not been internally validated; and it is further ORDERED that the defendant's motion to preclude the prosecution from offering expert testimony as to any statistical results obtained by using the random match probability on the composite minor component of mixture is granted. The above constitutes the decision and order of this Court"
His Honor ruled that whilst STRmix has been developmentally validated and is generally accepted as reliable within the scientific community the STRmix evidence was not admissible because of the lack of internal validation by NYSP.
Subsequent to the trial there have been some reports of different probabilistic genotyping software resulting in different conclusions for the DNA evidence. There were eleven alleles corresponding to the defendant across the three replicate profiles with no unexplained alleles when analysed using the NYSP validated analytical threshold. The RMP statistic for the match was 39 million. This statistic is known to not be conservative as it does not take into account the probability of dropout. The STRmix LR for the match was 335,000 (lower bound, taking into account all reasonable uncertainty in the statistic). Given the 11 matching and no mismatching alleles this LR is sensible based on sensitivity experiments undertaken using the Identifiler Plus profiling kit.