The chain of custody should be maintained at all times by all laboratories with access to the evidence.

The chain of custody is a recorded means of verifying where the evidence has travelled and who handled it before the trial. The reason for establishing a chain of custody is to prevent substitution of, tampering with, mistaking the identity of, damaging, altering, contaminating, misplacing or falsifying the evidence.

This principle and procedure creates legal integrity of the evidence. The chain of custody verifies both the legal integrity and the authenticity of all evidence. Without proof of an intact chain of custody, the evidence may be excluded from trial or afforded less weight by the trier of fact.

All laboratories that have access to the evidence must maintain accurate accountability of the chain of custody. It is best for the laboratory to keep the evidence in safe, properly controlled storage facilities and to limit the number of people who come in contact with the evidence.

Throughout the collection, handling, testing and storage procedures, strict protocols must be followed to ensure that the evidence remains verifiable in terms of authenticity and integrity. Each person that handles the evidence must be identified, and all periods of custody must be properly accounted for and recorded.

Failure to establish identity, authenticity, legal integrity, and a complete chain of custody for any item of evidence that passes through the laboratory may result in exclusion of the evidence or a limiting instruction to the jury regarding how to weigh the testimony.

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

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