[milk (2)]

I think he knows that, he's wondering if even detectives can get shot for it since you can't kill them unless you're defending yourself.

Yeah, I don't think Detectives are exempt from this. Least I know of, otherwise it'd be put that "Detectives are exempt from this" somewhere.
¯\_(ツ)_/¯

It's kind of common sense to not kill a detective though, especially when they are KOSd by another detective for simply opening the mine pit.

I shoot detectives for shooting me.