I think he interviews people for positions that are highly important + sensitive. As you note, what’s the likelihood that those people would end up being rogue operators. IMO not likely.
The interesting thing about Berman is, first, it’s SDNY (cesspool) and, second, the Cohen search warrant, if it was to cover additional material, would have to be worded exactly correct & proper to be sustained over time.
I’ve now had time to review the “disappearing shell casings” video and it’s inexplicable: https://mobile.twitter.com/incarnated__et/status/1107630794573377536?s=12