NCIS: Season 5, Episode 4

5 - 4: Identity Crisis

Ducky is angered when one of his research cadavers is revealed to have been a murder victim and was mistakenly tagged as a "John Doe" and donated to science. The deceased man is identified by the team as a career felon, who was working with the FBI to track down a man suspected of supplying people with new identities. NCIS works with the FBI to capture him and find the killer.