Vendetta

At a local bar, a man smashed a liquor bottle over a customer, killing him as a result. The killer wasn't a regular in the pub, so no one recognized him. Indeed the victim was well-known in the Big Apple for having caught a foul ball in a Yankee game that cost the team an entire season. Detectives started looking on Yankee fans: some had even set up a website against him. Forensics needed some time to examine the fingerprints; at the end the prints were in the system, matching to an inmate (David Warshofsky) who had just been released after twenty years in prison. He had no reason to kill the man: it had just been a reaction for having spent jail time for a murder he didn't commit (thanks to new technology there were proofs he was innocent). At the time, all was made up by a detectives (former partner of Green) who has held a grudge against him since the inmate boyhood. McCoy decided to prosecute the killer for another juvenile crime, trying to prove his criminal behavior.

This episode showed us a detective acting as a vigilante in order to make peace with himself. Anyway in the past when the DNA tests were not so accurate, this situation occurred frequently and abuse of power was easier than now.