One of the first questions an attorney with a new DNA case might ask is should the evidence be reanalyzed? As with all forensic questions, this depends on the circumstances of the case. The following will provide some guidelines to help you make that decision and also to plan you case strategy.

The most critical aspect of any review centers on the specifics of the laboratory results. The general questions to be answered include: 1) Do the data support the conclusions and 2) Do the conclusions concord with other data and information about the case? To answer these questions, it is necessary to review the laboratory report, the notes of the analyst that performed the work, the data upon which the conclusions are based, and also the police report, case synopsis and any presumptive testing that was done before DNA analysis. Because the significance of the conclusions rests, in part, on the population frequencies provided, the source of the frequencies, and evidence of their validity must be provided. Sometimes it is necessary to obtain frequencies for population groups not provided by the laboratory.

Depending on the results of the review, independent testing of any remaining sample may or may not be recommended. In most cases, it is more productive to direct both efforts and funding into the critical review defined above. It is more common for scientists to differ in the interpretation of results than to discount results completely. Unless an analysis is severely flawed, independent analysis would be unlikely to produce radically different results. Instances in which independent testing might be indicated include

1) retesting of a reference sample when the only evidence is a database hit
2) a finding of incorrect or inappropriate analysis by the laboratory
3) the possibility that testing of additional genetic markers might expose differences between the reference and evidence samples that were not detected in the original analysis
4) items of interest that were not tested by the laboratory.

Even if no glaring errors exist in the analysis, every case has a weak spot and this may be probed during cross-examination. A large part of the expert’s job is to educate the attorney about potentially complicated scientific material, and assist him in understanding how the advantages and disadvantages of any particular system apply to the case at hand. It is also useful if the expert can not only be available as a potential witness, but as a consultant during cross-examination of opposing counsel’s witnesses.