Yes I did. And a couple of days later, 2 detectives showed up, verified the item was in my possession and went on to the next person on their list. Incidentally they also marked the item by etching a number on it to make sure that they didn’t see it again, i.e., to rule out my cooperating with the person they were looking for.

what was it?

I would guess a firearm of some sort, as that's the only thing I can think of that would:

1.) be relevant to a police investigation 2.) be registered or associated with individuals 3.) have few enough of an exact thing in an area for the manual checking to be effective