If the story is true, there was federal surveillance outside the house 24/7 at that time (before the arrest).
Are you saying that if there were federal LEO's at his residency and they witnessed him take a bag of trash off premises and walk a ways (wearing gloves) in order to (probably illegally) dump into someone else's trash, they should have simply ignored this action of his?
What if that was a lot cleaning material from his car? Tiny amounts of DNA and fibers from the house could still be in that bag.
No LEO worth their salt, IF assigned to watch a potential murderer, is going to just sit and let him get out of sight. Once they see what he has done, why would they not grab that trash?? Sure, it could be nothing, but what if it's something? The job of such officers is to do exactly as it has been reported they did.
No gag order on the PA branch of federal enforcement, either.