Chain of Custody

Today I was watching CSI, when suddenly one of them open an evidence box to review an old case, when the evidence is reviewed in the evidence bag, there is a piece of paper stating "Chain of Custody" on it, where it is left blanked. I was like "wow", no wonder they can't solve the case, even if there is new evidence, the court wouldn't allow them to use the evidence as they have no idea on where the evidence had been. 

Photos linked from www.iape.org .