If the lye and ammonia aren’t illegal to possess, they probably can’t take it, and wouldn’t want to even if they could. (Of course I’m sure they noted it as circumstantial evidence in their case against the perpetrators.)

Cash is legal to possess, but that doesn't always stop the cops.

Right, but then it fails the second prong of my criteria.

You'd think - same with the vinyl records for that matter - that it would be seized as evidence. I mean that underwear could be from a murder victim or somesuch.

But that's speaking in idealisms, in practice they probably didn't give a shit and moved on to other things. Just another car crash / drug case.

I think it depends on the location.

My car was stolen about 15 years ago in Seattle. The block I lived on at the time was a popular place for car thieves to both pick up and drop off cars.[1] When it was recovered, there were a bunch of stolen credit/debit cards and other potential evidence inside.

The officer who took the report said I could try calling the detectives who were responsible for that kind of investigation, but he didn't think it would go anywhere, because either the mayor or the chief of police (I don't remember which) had told them to deprioritize car thefts. Sure enough, calls to that line went straight to voicemail, and I couldn't even get a call back telling me they weren't interested.

[1] The day I discovered my car was stolen, there was a silver Civic parked across from it in the spot where a neighbour usually parked her silver Civic. That day, it was not hers. It was a nearly-identical silver Civic that the car thieves had ditched before stealing my car.