Retention of Samples for Future Testing

It is highly recommended that samples be split whenever possible before and during the testing process. The laboratory should only test the amount of sample needed to obtain reliable and interpretable test results; any untested sample should be retained for possible future testing. Once DNA is obtained from a sample, the laboratory should assess the quality and quantity of the DNA, whenever possible, and consult with the individual who submitted the evidence regarding tests to be done. Again, only the amount of DNA required to obtain reliable and interpretable test results should be consumed in the testing; any remaining DNA should be preserved for future testing. The preserved and untested sample remains available for:

  • Repeat testing by opposing counsel. The prosecuting attorney or the defense attorney may request a portion of the untested sample to repeat the testing or have additional testing done in a laboratory of his or her choice.
  • Retesting if there is a problem. If a problem arose in interpreting the results, or an error occurred during the first test, an untested portion of the sample will be available to repeat the test.
  • Additional testing to exclude a falsely accused individual. Testing at additional regions of the DNA may be required to exclude a falsely accused individual. Untested areas of the sample or remaining DNA may be used for these additional tests.
  • Additional testing to aid in the interpretation of the test results. In situations where more information would be helpful for interpreting the test results, testing at additional regions of the DNA is advised. For example, the additional tests could confirm that the DNA sample contains a mixture of DNA from two or more individuals and may aid in determining whether the defendant can be excluded as one source of the DNA.
  • Future testing when new technologies become available. A portion of the sample and the DNA should always be retained, whenever possible, for testing in the future when additional technologies become available. Many samples that proved inconclusive with RFLP testing have been retested using PCR and the results have been exonerative. In contrast, samples that were consumed during RFLP testing are now not available to the defendant for PCR testing. Samples that were inconclusive with nuclear PCR testing may be suitable for mitochondrial DNA testing and could lead to exonerations in the future. Other tests not now available could be used in the future to confirm convictions or to exonerate defendants.
  • Additional testing to aid in identification of the perpetrator when the convicted individual has been excluded. If the DNA test performed in a postconviction relief case results in the exclusion of, and thereby establishes the innocence of, the convicted individual, the prosecutor may require additional testing of the evidence sample to aid in the identification and prosecution of the real perpetrator of the crime.

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