Com. v. Sok

• Decision Date: 25 August 1997
• Citation: 683 N.E.2d 671,425 Mass. 787
• Parties: COMMONWEALTH v. Vao SOK (and thirteen companion cases 1 ).
• Court: United States State Supreme Judicial Court of Massachusetts Supreme Court

Page 671

683 N.E.2d 671

425 Mass. 787

COMMONWEALTH v. Vao SOK (and thirteen companion cases ¹).

Supreme Judicial Court of Massachusetts,

Suffolk.

Argued May 8, 1997.

Decided Aug. 25, 1997.

Kelly Ann Downes, Assistant District Attorney, for the Commonwealth.

James L. Sultan, Boston, for Henry Juan Williams.

Nona E. Walker, Committee for Public Counsel Services, for Herdius Evans.

Elliot M. Weinstein, Boston, for Vao Sok, & Benjamin Entine, for James Ware, were present but did not argue.

Before WILKINS, C.J., and ABRAMS, O'CONNOR, GREANEY and MARSHALL, JJ.

GREANEY, Justice.

This interlocutory appeal, in which the Commonwealth is the appellant, arises from three murder proceedings in the Superior Court: the defendant Vao Sok is charged with the kidnapping, rape, and murder of Anmorian Or; the defendant Henry Juan Williams is charged with the murder and armed assault of Zachariah Johnson; and the defendants Herdius Evans and James Ware are jointly charged with the armed robbery and murder of Allan Lawrence Hill (and with other crimes). The Commonwealth sought to introduce in evidence against each defendant deoxyribonucleic acid (DNA) test results derived from the polymerase chain reaction (PCR) method. Citing Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993), the defendant Evans filed a "motion in limine to exclude evidence of DNA testing or in the alternative to conduct a Daubert hearing," which the other defendants joined. At the request of the Regional Administrative Justice, a judge in the Superior Court conducted an evidentiary hearing on the defendants' consolidated claims. The judge subsequently entered a memorandum and order in which he ruled that the results of the DQa PCR-based DNA testing could be admitted in evidence against each defendant, but that the results of the Polymarker (PM) PCR-based DNA testing and the D1S80 PCR-based DNA testing should be excluded in each case. ² The Commonwealth filed a petition for relief under G.L. c. 211, § 3, challenging the judge's decision with respect to the PM and D1S80 test results. The petition was considered by a single justice, who reserved and reported the cases along with three questions noted below. ³ Since the entire matter is before us, we can resolve the issues without the necessity of framing responses to the reported questions. We conclude that the PCR-based tests at issue in this case meet the test of scientific reliability under Commonwealth v. Lanigan, 419 Mass. 15, 24, 26, 641 N.E.2d 1342 (1994), and that there must be further proceedings in the Superior Court to decide whether the PM and D1S80 test results in these cases should be admitted in evidence.

1. Background. (a) The genetic and molecular basis of DNA typing is described in the appendix to our decision in Commonwealth v. Curnin, 409 Mass. 218, 227-231, 565 N.E.2d 440 (1991). There we pointed out that forensic DNA testing is directed at the examination and comparison of the characteristics of several "highly polymorphic alleles." The Curnin case described the meaning of the scientific term "highly polymorphic alleles" as follows:

"A single DNA molecule contains approximately three billion rungs, or base pairs. Certain types of human genes ... can occur in alternate forms (that is, with differing sequences of base pairs), each of which is capable of occupying a gene's position on the DNA ladder. These alternate forms of genes are called 'alleles,' and are highly variable from one person to another. Alleles of a particular gene contain a different number of base pairs, and therefore are of different lengths.

"Most of the sequences of base pairs in all human DNA molecules are identical. However, roughly three million base pairs are alleles that vary in sequence among humans. The areas on the DNA ladder in which the DNA sequence varies are called 'polymorphic sites.' Some such sites are more polymorphic than others. Forensic DNA testing makes use of sites which are 'highly polymorphic.' " Curnin, supra at 228, 565 N.E.2d 440. ⁴

The variations or polymorphisms between alleles at a particular location may occur either in the particular sequence of the base pairs at a particular locus or in the length of a DNA fragment between two defined endpoints. It is the ability to detect and compare the alleles at a particular locus in one sample of DNA with the alleles at that same locus in another sample of DNA that forms the basis for the use of the technology in a forensic setting.

There are different methods used in DNA forensic testing including Restriction Fragment Length Polymorphism (RFLP) and PCR amplification and allele identification. RFLP analysis requires a larger segment of DNA than does PCR analysis and involves a time-consuming testing process. RFLP targets loci on DNA molecules that are known to have different lengths because of variations in the number of times that a sequence of base pairs is repeated. These loci are referred to as variable number tandem repeats (VNTRs). RFLP uses the seven-stage process described in Commonwealth v. Curnin, supra at 228-230, 565 N.E.2d 440, to examine and compare the length of various alleles and then engages in a series of calculations to determine how often those combinations of alleles occur in a given population. The RFLP process was not used in the cases before us.

PCR-based testing is an alternative method of analyzing forensic DNA samples that compares polymorphic DNA sequences through "allele-specific probe analysis," a very different process from RFLP, which looks at the length of the DNA sequence. The goal of a PCR-based approach is to determine whether certain alleles are actually present or absent in a sample. Two DNA samples taken from the same individual will contain the same alleles. Samples from different individuals are apt to contain different alleles. Thus, finding the same alleles in two different samples supports the conclusion that the samples have a common source. As with RFLP, if a match is identified, calculations are performed to determine how often such a match is likely to occur in the population. Where an individual's sample matches a provided sample of DNA, the individual cannot definitely be excluded as the possible source of the provided sample of DNA, but where key alleles do not match, the individual is excluded as the source.

PCR-based analysis involves the making of millions of copies of particular short segments of DNA in an amplification process, similar to the mechanism by which DNA normally replicates itself. ⁵ After the segments are replicated, different genetic marker typing tests are performed, depending on the particular polymorphic locus being probed. The tests in the cases before us involved three polymorphic loci: the DQA1; the polymarker loci ⁶; and the D1S80 (each locus was not examined for each defendant). Different typing kits were used to amplify and detect the genetic markers. ⁷ After the genetic markers have been identified, the DNA profile is compared to another profile from a known source. If an appropriate correlation appears, a statistical analysis is performed, based on population databases, and the probability of a random match for a particular sequence is estimated from the frequency with which that sequence appears in the relevant databases.

PCR-based testing is extremely valuable for forensic science. It permits DNA profiling of samples containing much smaller quantities of DNA--such as saliva on a cigarette butt--than can be tested by the RFLP method, and test results are available promptly, often within twenty-four hours. "[M]ost PCR tests permit exact identification of each allele at a particular locus, eliminating the measurement imprecision of RFLP" and its accompanying statistical analysis. United States v. Lowe, 954 F.Supp. 401, 409 (D.Mass.1996). "Indeed, defendants in criminal cases have been known to be as interested in securing [the] use [of PCR analysis] in this context as prosecutors." ⁸ Id., and cases cited.

(b) All the DNA testing in the cases before us was done at CBR Laboratories in Boston (CBR) in 1994 and 1995. CBR is a wholly owned subsidiary of the Center for Blood Research, a non-profit research institution affiliated with Harvard Medical School. The testing was performed for the State police or Boston police department that had investigated the crimes by Dr. David H. Bing, the director of CBR, and two of his assistants. PCR amplification and typing were performed, as deemed appropriate in each case, by means of three available scientific DNA genetic marker kits: the Amplitype HLA DQa Amplification and Typing Kit ⁹; the AmpliType PM PCR Amplification and Typing Kit; and the AmpliFLP D1S80 PCR Amplification Kit. These kits are marketed by Perkin-Elmer Corporation, Inc., under licenses from Roche Molecular Systems, which holds the patents on the kits. In his memorandum, the judge described in considerable detail the steps taken in the use of the kits, and explicitly set forth the testing process in each case, the results of the tests, and Dr. Bing's conclusions, as reported to the investigating authorities.

We need not summarize the contents of the reports beyond noting the following. The Vao Sok and Williams cases involved test results from the DQA1, PM, and D1S80 loci, and the Evans and Ware cases involved results from the DQA1 and PM loci. Each report stated conclusions as to whether the particular defendant could or could not be excluded as the donor of sample DNA that had been extracted from the different items provided to CBR by the police. Where relevant, the reports also contained an estimation of population frequencies. It is important to point out here that the evidentiary value of PCR-based tests lies in their combination with one another. The likelihood of a coincidental match between different samples of DNA is relatively high if only DQA1 testing is done. When that testing is...