Expert witness
Chain of custody

It is important that expert witnesses who handle evidence maintain a proper chain of custody such that they are able to authenticate the evidence, prove that it is what they represent it to be, when testifying at trial. Most notably in the context of a criminal prosecution, an expert witness who evaluates or examines an item pertinent to an investigation or case evaluation may add an entry to a "chain of custody" document, a form that contains the item's description, the time and date of release for all prior custodians of the item, and the time and date of release to the witness.
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