Care should be taken in selecting samples for testing that will give meaningful/useful results for a particular case. There is no point in testing samples that have no relevance to the crime for which an individual was convicted. (See discussion of category 5 cases in Framework for Analysis.) It may be important to reevaluate/analyze previously collected evidence samples to determine if there are: 1) other relevant evidence samples that could be tested (e.g., slides made from vaginal or cervical swabs, if no vaginal swab remains for testing); 2) samples containing stains or other biological samples that had not been detected previously; or 3) samples that were unsuitable for testing with previous techniques but may give conclusive results with currently available DNA tests (e.g., very small blood or semen stains, hair shafts).
The availability of and need for samples from known individuals who should be tested for exclusionary purposes will need to be carefully considered. For example, in sexual assault cases in which the defendant is excluded as a donor of the DNA, it is imperative that a sample from the victim and any known consensual partner(s) be tested in order for that exclusionary result to provide exculpatory evidence. Additionally, the testing of the victim's sample in sexual assault cases can serve as a built-in control to confirm that the testing has been performed correctly and that the questioned sample is, in fact, linked to that victim.
It is advisable that samples be split whenever possible. This permits a portion of the sample to be available for:
- Retesting by opposing counsel.
- Retesting if there is a problem in the testing and it needs to be repeated.
- Additional testing for aiding in the interpretation of test results (e.g., mixtures), for providing more tests for exclusionary purposes, or for aiding in the identification of the true perpetrator when the convicted individual is excluded in postconviction testing.
- Future testing when new technologies become available.
For additional discussion, see the Selection of Samples for Testing section in Recommendations for Laboratory Personnel.
Go to the Next Section: Testing of Samples Deposited on Various Substrates
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