Shaun McLean works as a criminal staff attorney in the Massachusetts Appeals Court. She previously served as an assistant district attorney in the appeals unit of the Bristol County District Attorney's Office and in the district court and appellate unit of the Northwestern District Attorney's Office. She worked in private practice with an emphasis on criminal defense work. The views expressed in this article are solely those of the author, and are not intended to represent the views, opinions or policies of any of the aforementioned entities.
Over the past 12 years in Massachusetts, DNA (deoxyribonucleic acid) evidence has become a well-known and powerful tool for use by both the prosecution and the defense. Many aspects of this evidence have been judicially examined and approved, but there is at least one area that remains unchallenged - the manner in which DNA testing is performed and the interpretation of those test's results in a particular case. Considering the weight that this evidence carries in our courtrooms, it is critically important to insure, rather than assume, that the testing itself is scientifically reliable.
To put this issue in context, it is important to understand what aspects of DNA testing have already been found to be reliable. Generally speaking, relevant DNA evidence is created in a two-step process. First, the DNA sample of the suspect and the DNA sample from the crime scene are put through a series of tests to isolate a particular region of the DNA molecule and to identify the genetic material at that location, which is variable from person to person. See generally Commonwealth v. Sok, 425 Mass. 787, 789-790 (1997). The two samples are compared and when a "match" of the variable genetic material is detected, the next step is undertaken. In the second step, the frequency with which that match occurs in the general population is determined through the application of certain statistical calculations. Commonwealth v. Lanigan, 419 Mass. 15 (1994)(Lanigan II). The results, standing alone, can carry the strength of a jury verdict. For example, it is easy to understand how a match - between DNA evidence found at the crime scene and the defendant's DNA - that occurs in only one in 160 million people would dwarf almost any other evidence in the case (absent eyewitness testimony or a confession). See Commonwealth v. Hill, 54 Mass. App. Ct. 690, 694 (2002).
Given the strength of the statistical aspect of such numbers as one in 160 million, it is not surprising that when Massachusetts' courts first scrutinized DNA evidence, the evidence was initially rejected, not on grounds of novelty or unreliability of the scientific principles in the testing, but because of concerns related to the statistical reliability of the probability calculations. See Commonwealth v. Curnin, 409 Mass. 218, 221-222 (1991)(Overlooking the propriety of the DNA testing, the court rejected the DNA evidence because the statistical analysis that was applied to the test results had not been shown to be reliable); Commonwealth v. Lanigan, 413 Mass. 154 (1992)(Lanigan I)(same).
After working through concerns related to the statistical evidence, and approving particular calculations, Lanigan II, 419 Mass. at 27, the courts turned to the reliability of particular DNA testing methods used to identify the genetic material. While the nature of the inquiry regarding whether such novel scientific evidence should be admitted has undergone many of its own changes, from Frye v. United States, 293 F. 1013 (D.C.Cir.1923) to Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) to Canavan's Case, 432 Mass. 304, 309-312 (2000), this inquiry, distilled to its essence, turns on a consideration of whether the scientific methodology is reliable.
In relation to DNA evidence, that inquiry produced judicial approval of a number of DNA testing procedures. For example, DNA profiling evidence from RFLP (Restriction Fragment Length Polymorphism) analysis has been held to be a scientifically valid methodology. Commonwealth v. Dagget, 416 Mass. 347, 350 n.1 (1993). In addition, PCR (polymerase chain reaction) based testing conducted at the PM and DQA1 loci and at four loci containing variable short tandem repeats (STRs) has been held to be scientifically reliable. Commonwealth v. Rosier, 425 Mass. 807, 811-812 (1997); and Commonwealth v. Sok, 425 Mass. 787, 790-795, 800-801 & n's. 5-11 (1997).
While the reliability of both the probability calculations and the principles and methodologies involved in DNA testing may still be challenged, particularly as scientific principles evolve, Canavan's Case, 432 Mass. at 311, the initial battles over the reliability of this novel scientific evidence have concluded. The result is a resounding acceptance of certain DNA tests and particular statistical calculations.
The area related to DNA evidence in which there has not yet been any appellate decisions however, concerns the testing procedures used in a particular case. From the first appearance of DNA evidence in appellate case law, the courts have recognized the importance of insuring that the testing done in each case was reliably performed. Commonwealth v. Curnin, 409 Mass. at 222 n.7. ("Future challenges should focus on the soundness of and general acceptance of the particular testing process for forensic use, and, if raised, on the proper implementation of that process in the given case."); see also Canavan's Case, 432 Mass. at 309-312; Commonwealth v. Hill, 54 Mass. App. Ct. at 697-698.
Anticipating that the testing used in a given case would be challenged, the decisional law set forth the precise manner by which to raise an issue concerning the testing procedures. Objections to DNA testing procedures on grounds that the tests may have been improperly or unreliably performed, must be preserved by filing "an appropriate pretrial motion stating the grounds for the objections and request a hearing..." Commonwealth v. Hill, 54 Mass. App. Ct. at 698 citing Commonwealth v. Sparks, 433 Mass. at 659 (other citations omitted.)
While there are hints in the decisional law that attempts to challenge the testing procedures have been made, a review of the cases show that the substantive issues were never reached. For example, in Commonwealth v. Sparks, the defendant argued on appeal that the DNA testing kits used by the laboratory conducting the tests were contaminated. 433 Mass. at 659. The court ruled that because the defendant had filed neither a pretrial motion raising this claim, nor a motion for new trial, it is too late to "raise objections concerning the reliability of the testing..." Id. at 660.
In Commonwealth v. Hill, the defendant's argument suggested that the DNA evidence offered by the expert at trial was based on improperly or unreliably performed testing procedures. 54 Mass. App. Ct. at 697. The court again however, rejected the claim because no appropriate pretrial motion had been filed, nor was any other proof of the allegation adduced at trial or on appeal. Contrast Id. at 698 (Defense expert did provide credible evidence that one of the three DNA tests had been contaminated.)
Most recently, in Commonwealth v. Evans, 438 Mass. 142, 153-154 (2002), the defense clearly attempted to review the testing procedure by retaining two experts to oversee the process. In turn, defense counsel attacked the reliability of the tests by cross-examining the commonwealth's expert, but never called the defense experts to testify. As a result, the commonwealth was properly permitted to elicit evidence that suggested the tests were more likely to have been fairly conducted in the presence of the defense experts.
With respect to the admission of other scientific evidence, the courts have not hesitated to impose requirements on the proponent of the evidence to show that the scientific testing was reliably conducted. For example, in order for the chemical analysis of the breath of a defendant to be admissible against that person in a case involving driving under the influence, it must be shown that the test was done by a certified operator, on a certified device according to methods approved by the Secretary of Public Safety. Commonwealth v. Barbeau, 411 Mass. 782, 784 (1992); and see G.L. c. 90, ß 24K. The Secretary of Public Safety detailed those methods in regulations that specify precisely how to assess and validate the accuracy of Breathalyzer results obtained by a breath test operator. See generally 501 CMR 2.00 et seq.
While in the case of breath testing, the scientific instruments are usually owned, as well as operated by the local or state police and thus, more readily amenable to state control and regulation, the basis for admitting scientific evidence does depend on the whether the state or private industry is performing the test. Rather, the same evidentiary standards apply to all scientific evidence. See generally Commonwealth v. Brooks, 366 Mass. 423 (1974); Commonwealth v. Neal, 392 Mass. 1 (1984); and Department of Youth Servs. v. A Juvenile, 398 Mass. 516 (1986). Thus, no less ought to be required of the proponent of DNA evidence, in terms of showing that the test was reliably conducted, than is required of the proponent of breath testing results in a drunk driving case.
The need for such assurance is also important because DNA testing is very complex. Isolating the region of each DNA sample to be examined, identifying the genetic material at that region, and then comparing the genetic material from each sample to determine if there is a "match" involves a significant degree of subjective judgment. See Commonwealth v. Sok, 425 Mass. at 795 (trial judge concluded after evidentiary hearing that "[t]here is a considerable amount of subjective judgment involved in the interpretation of the results of PCR-based tests, and experience is necessary to interpret the data."); and see generally, Commonwealth v. Curnin, 409 Mass. 218 (appendix). Apart from legitimate differences of opinion about test results, simple inadvertence or mistake may lead to potential errors in any one of the steps involved in this procedure.
Despite these possibilities and the clear anticipation in the decisional law that the tests would be challenged, there has not been an appellate decision to date where a credible challenge has been made to the testing procedures used in a particular case or alternatively, that a protocol has been established and is invoked in each DNA test to insure reliable test results. The suggestion in this article, that a showing must be made that each test has been reliably conducted, is not to underestimate the difficulty, or even the expense, of the task. It is clear that laboratories such as Cellmark Diagnostics (Cellmark), one of the few laboratories that provide forensic DNA testing, have already established their reputation in the appellate courts for excellent scientific work. See Commonwealth v. Sparks, 433 Mass. at 658; Commonwealth v. Hill, 54 Mass. App. Ct. at 693. An outstanding reputation however, cannot serve as substitute for a substantive review of each aspect of the testing in a particular case.
DNA evidence is one of the most powerful evidentiary tools to become available in the history of criminal litigation. The evidence demands the highest degree of scrutiny that can be brought to bear and that includes a rigorous review of the highly complex procedures used to create it in each particular case. Anything less creates the risk that our criminal justice system will be converted to one driven by scientific test results, rather than legal principles and common sense.