Lmao, at first I only read the part ronito quoted here, and thought "shitty handling of evidence? Hmm, what, is the officer with the knife in a fucking traffic unit?"
Then I clicked the link:
At a news conference at LAPD headquarters Friday morning, Capt. Andy Neiman said the officer was a traffic cop and was working on a movie set when he was given the knife.

I mean, I don't know the stereotype/joke here...
It's less a stereotype, than me quickly going "hmm, ignoring the gross incompetence anyway, what sort of officer might be typically oblivious to the importance of chain of custody? Not any major crime/drugs/homicide/plainclothes officer, obviously....probably not a well-rounded beat cop....aha! Traffic! They focus on road safety, write driving infraction tickets that are based solely on their own observations, lay impaired driving charges, again based on their observations and breathalyzer results, lay charges in collisions based on an analysis of the scene at the scene.....not necessarily a lot of exhibit handling requirements in there...."
and then it turns out my snap guess was right.
