Criminal law - Supreme Judicial Court of Massachusetts fails to require statistical analysis for nonexclusion DNA test results.

• Author: Adam, Kevin C.

Criminal Law--Supreme Judicial Court of Massachusetts Fails to Require Statistical Analysis for Nonexclusion DNA Test Results--Commonwealth v. Mattei, 920 N.E.2d 845 (Mass. 2010).

Massachusetts grants judges broad discretion when determining the relevancy of evidence. (1) The Massachusetts Guide to Evidence Section 403 (Section 403) states that relevant evidence is admissible unless the trial judge believes the probative value of the evidence is substantially outweighed by the danger of unfair prejudice to the defendant. (2) Massachusetts judges apply a case-by-case approach in weighing the prejudicial effect of deoxyribonucleic acid (DNA) test results presented to a jury absent supporting testimony regarding the statistical accuracy of such results. (3) In Commonwealth v. Mattei, (4) the Massachusetts Supreme Judicial Court (SJC) addressed whether DNA test results that failed to exclude an individual as a possible contributor to the DNA sample were admissible without an accompanying probability analysis. (5) Although the SJC held that the nonexclusion test results were improperly admitted, it failed to require that supporting statistical testimony is always necessary to admit such results. (6)

On April 2, 2004, a jury in Massachusetts Superior Court convicted Alexander Mattei of assault with the intent to commit rape. (7) At trial, the Commonwealth's forensic chemist testified that two of the samples gathered contained a mixture of DNA that did not result in an exact match with the victim or the defendant, but could not exclude either individual as a possible contributor. (8) over the objection of Mattei's counsel, the court admitted the forensic chemist's testimony without an accompanying statistical explanation regarding the probability of a random sample resulting in a similar nonexclusion. (9) The Commonwealth later relied on the testimony of the forensic chemist to assert that the test results, which were partially consistent with the samples, could link the defendant to the crime. (10)

The Massachusetts Appeals Court upheld the admission of the evidence despite the lack of a statistical explanation, reasoning that the evidence was admissible because it was "descriptive of the individual" and was not presented to the jury as a match. (11) The appeals court failed to differentiate between nonexclusion and inconclusive test results when addressing the need for supporting statistical testimony. (12) On appeal, the SJC differentiated between these two types of test results, refusing to analyze a nonexclusion in the same light as a test that amounted to "no result." (13) The SJC ordered a new trial, holding that the trial court erred in admitting the nonexclusion DNA evidence without additional statistical support. (14)

In Massachusetts, courts determine the admissibility of DNA evidence--as well as most other forms of evidence--primarily by analyzing whether the evidence is relevant. (15) Frequently, DNA evidence is relevant in criminal trials where the evidence is used to identify the alleged perpetrator. (16) Massachusetts courts require expert testimony for the admission of DNA test results, but are divided on whether additional information is necessary to explain the statistical significance of the results. (17)

Massachusetts courts have held that where a DNA test results in a match, the result is inadmissible without an accompanying statistical explanation as to the probability of the match occurring by coincidence. (18) When a DNA test determines that there is no match, the results may be admitted without an accompanying probability analysis, but only when the results are probative of a specific issue of consequence in the case. (19) Massachusetts grants judges broad discretion with respect to whether this type of additional statistical information is necessary when admitting inconclusive test results. (20) Unfortunately, this broad discretion results in a case-by-case approach that has lead to conflicting results. (21)

Massachusetts courts have failed to differentiate between nonexclusion DNA test results--results failing to exclude an individual as a possible contributor--from inconclusive test results, often using the two terms interchangeably. (22) In contrast, other states that require statistical support to accompany matching results do not group together nonexclusion and inconclusive results, but rather they categorize both as being "consistent" with the test sample. (23) Moreover, other states that allow for the admission of DNA tests resulting in a match without supporting statistical explanation do not differentiate between a match and a nonexclusion. (24) This approach is based on the theory that a nonexclusion--a result failing to exclude a defendant--also indicates that a match occurred at some allele sites; therefore, the courts should interpret such a result as a type of match, rather than an inconclusive test producing no determinable result. (25)

In Commonwealth v. Mattei, (26) the SJC held that the probative value of the DNA test results, which failed to exclude the defendant as a possible contributor, was substantially outweighed by the prejudicial effect of asking the jury to interpret the results without the assistance of expert testimony. (27) In reaching its decision, the SJC differentiated between inconclusive results and nonexclusion results. (28) The court rejected the Commonwealth's argument that the DNA test results, which were not a match, should be admissible to provide the jury with "descriptive information" about the possible contributor. (29) The SJC determined that admission of the nonexclusion results, without accompanying statistical explanation, unfairly prejudiced the defendant because it forced the jury to evaluate the significance of the results without the assistance of statistical testimony, encouraging jurors to act as their own experts. (30)

In Commonwealth v. Mattei, (31) the SJC had an opportunity to clarify the confusion created by the case-by-case approach previously applied by Massachusetts courts regarding the requirement of supporting statistical analysis when admitting DNA test results that were not a match. (32) The court correctly addressed the issue of possible prejudice by weighing the probative value of the nonexclusion result against its prejudicial effect, but in doing so, it avoided the logical conclusion that should have stemmed from its analysis. (33) Consequently, the SJC failed to establish a clear rule requiring statistical support to accompany any DNA match or nonexclusion result. (34) This decision will likely result in further confusion and conflicting results at the trial court level. (35)

Massachusetts courts require all DNA tests that result in a match to be accompanied by supporting statistical testimony. (36) The SJC recognized in Mattei that the same underlying reasoning requiring statistical information when admitting a match should also apply to a nonexclusion, given the possibility of jury confusion and prejudice that exists with both. (37) Moreover, the SJC stated that admitting a nonexclusion without accompanying statistics "creates a greater risk of misleading the jury and unfairly prejudicing the defendant" than admitting a match without statistical support. (38) Given this concern, the logical conclusion would be to require statistical support for all DNA tests that result in either a match or a nonexclusion. (39) Instead, the SJC chose to analyze admissibility solely using Section 403 to weigh the probative value of the evidence against its prejudicial effect, circumventing the issue of whether statistical support is required to admit future nonexclusion test results. (40)

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