For purposes of litigation, regulatory agencies must be able to prove the legal integrity of all samples and data introduced as evidence. This means it is necessary to have an accurate written record to track the possession, handling, and location of samples and data from collection through reporting. Verification of who has possessed the samples and data and where the samples have been is easier if you follow chain-of-custody procedures.
Since there is no way to know in advance which samples and data may be involved in litigation, you should always follow chain-of-custody procedures whenever samples and data are collected, transferred, stored, analyzed, or destroyed. Besides, it is good scientific practice to do so. A secure chain of custody, combined with the use of proper analytical methods and techniques, is necessary for a legally defensible reporting of the sample.