Right now the FBI is shutting out state law enforcement, but that does not prevent the state from charging him anyway, now or in the future. It may come down to the prosecutor bringing a case with the multiple videos and eyewitnesses, and making a bet that they don’t need the actual gun or the other pieces of evidence the FBI has commandeered to make their case.

They have to be very careful how they go about it, but that option remains open forever, as others have pointed out. This murder will never NOT be hanging over that thug’s worthless sociopathic head.