In PRESERVE THE PHYSICAL EVIDENCE!, electrical expert witness Roger L. Boyell, writes:
As soon as you believe a legal action might be initiated, take pains to preserve whatever physical evidence may be relevant. Send in an investigator, take many photographs, expedite the discovery process. Alteration or disguise of potential physical evidence need not be on purpose. Damage gets repaired, defects are corrected during routine maintenance, new features and devices are incorporated in machinery, apparatus undergoes corrosion and decay. Copies are not always exact replicas. Computer records can be overwritten with no intent of spoliation.
The lesson is to promptly identify and preserve whatever evidence might later become useful for presentation in the forum: equipment, photographs, test results, written records, videotapes, lab samples. Physical evidence never improves its usefulness to litigation with the passage of time.