Previous Testing: Was It Done? What Do the Tests Mean?

To aid in the evaluation of a case and to assess the need and feasibility of doing DNA tests in postconviction cases, it is imperative that the following information be obtained regarding any previous testing that was done:

What items of evidence existed at the time of the original trial and what type of analyses or tests were done on that evidence?

This would include any microscopic or serological analysis (e.g., identification of sperm; detection of semen, saliva, or human blood; hair comparison; ABO blood typing; typing of other protein markers) as well as any DNA tests. This information should be obtained regardless of whether the results were used in the trial and regardless of whether the evidence still exists for retesting. This information may aid in determining whether to proceed with DNA testing in a postconviction relief case or categorize the case as one in which DNA testing would be meaningless (e.g., no biological sample exists on the evidence or sufficient conclusive restriction fragment length polymorphism (RFLP) results exist). This information also may aid in the identification of additional evidence and in locating the evidence for testing.

What are the limitations of the tests that were performed?

It is important to understand what the previous test results really mean and whether those results could have been obtained if another individual other than the alleged donor was the source of the sample. For instance, ABO blood testing and/or DQa. PCR test results alone are not sufficiently discriminating such that a falsely accused individual would necessarily be excluded with these tests; additional DNA testing may be suggested in these cases. Conversely, if a multiple-probe RFLP match was obtained previously, additional testing may not be advised unless there is a strong indication of an error in the testing.

Were the results used at trial and, if they were not used, what was the reason?

If the test results were used at the trial, it is important to understand how the results were used in the case and whether they were accurately presented to the trier-of-fact. Test results may not have been presented at the trial because they were obtained at a late date, or because they were inconclusive or not supportive for either the prosecution or defense position. Alternatively, test results may not have been presented at the trial because the prosecution reasoned that the other evidence in the case was overwhelming and chose not to admit the evidence. There are many cases in this country where four- or five-probe RFLP results have been obtained but not used at a trial for various reasons (e.g., the attorney did not want to go through an admissibility hearing, a witness was not available, or the results were obtained too late to provide in discovery).

Were there any test results reported to be inconclusive and, if so, what were the reasons for the inconclusive results?

The changes in expertise and technology available for forensic DNA testing may require the reexamination of previously inconclusive test results and/or retesting of the samples. Due to the technical limitations of various tests and the variation in expertise of scientists, some laboratories take a more "conservative" approach than others when reporting test results and report a result as inconclusive when other experts may report the result as an inclusion or exclusion. This has been especially true for DNA test results when a mixture of DNA from two or more individuals has been obtained. No results or inconclusive results (because only weak or partial results were obtained) may have been reported for a sample that might yield conclusive results if other tests are attempted. For example, samples that yielded no or uninterpretable results with RFLP testing may well yield interpretable results with nuclear PCR testing. Similarly, samples that were unsuitable for nuclear PCR testing may yield results with mitochondrial DNA testing.

In older cases appropriate evidentiary samples or standards may not have been available or recognized as relevant and/or were unsuitable for testing with DNA tests available at that time. Reevaluation of collected evidence samples may lead to the identification of other relevant biological samples that had been previously undetected, or previously tested items that may give conclusive results with current techniques. Additional testing with newer, more sensitive, and more discriminating tests (e.g., short tandem repeats (STRs), Y chromosome) may help resolve previously inconclusive test results where the evidence sample and the known standards from the victim and suspect all gave the same test results, or evidentiary samples previously yielded no DNA foreign to the victim (e.g., vaginal swab, breast swab, fingernail clippings). Identification and testing with current techniques of other or newly discovered evidence samples, standards, or relatives of the victim may lead to conclusive results.

Are copies of the laboratory case notes, including any original photographs taken and films of any DNA test results, available for review by an expert?

? In many of the situations listed above, it will be necessary for an expert to review the data previously obtained by a laboratory in order for that expert to advise an attorney regarding the need for retesting and/or the types of tests to request.

It is recommended that one or both attorneys, and/or the court, seek the advice of an expert who can provide information regarding the issues and questions raised above. The expert may need to obtain copies of the previous test results and laboratory case notes for review in order to adequately advise the attorney/court. Whenever possible the appropriate attorney should obtain the needed materials and provide them to opposing counsel as requested. If additional testing is to be performed in a postconviction case, it may be important to consider what comparisons will need to be made with already existing results (e.g., for third-party individuals, for comparison with database records, for comparison with other cases). Also see Recommendations for Laboratory Personnel for additional information.