I cannot possibly give you or any other nit picker an answer that will fit all officers and all situations. Could you?
I once knew a cop, actually an in-law, who arrested a guy for “assalt and battrie”. I’m serious.
How many cops would turn down a fed who “asked” him or her to “help them out” and go bust some doors down and confiscate some guns? They’d feel like they were CIA, FBI, KGB and all them other letters.