Whenever possible, a portion of biological, toxicological or other samples should be retained for future testing. In situations where the entire sample may be consumed in the testing process, the analyst should notify and/or consult, as prescribed by their policy, and document the events in the case file.

Evidence items should be maintained at the lab while testing is ongoing. Labs should keep documentation of all personnel with access to the evidence while it is at the lab on a chain of custody form initiated by the submitting agency, maintained by the lab, and transferred to the agency that takes final possession of the evidence.

For more on chain of custody issues, see Sources of Scientific Evidence, Topic 2; Testing or Evaluating Evidence and Writing Reports .

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