Yeah, I'm sure law enforcement would never abuse such a back door for parallel prosecution or to circumvent a warrant. *eye roll* Our Government and law enforcement already have too much power that rages unchecked, despite the promise of usually nonexistent oversight.
Just recently they published secret NSA programs, one of which specifically targeted Americans. http://www.zdnet.com/article/ragtime-program-appear-in-nsa-leaked-files/ Where is the oversight? Congress, so really no oversight.