Right before Elvis finds Justin's body, a pair of reading glasses hang from his collar. A few shots later, they're gone.
The position of Gary's fingers on the detonator between shots.
When Dylan is pointing the Glock handgun at Gary, it is not in a ready-to-fire condition. (The trigger is in a state where it has already been pulled but not reset. This happens after pulling the trigger with no round in the chamber.)
He never drops the detonator. It is in his hand during the entire sequence. (1:18:29) He is cupping the detonator and using his middle two fingers to rip paper and writes the names with his other hand. The detonator is in his hand the entire time - he does not drop it or put it down in any way, shape or form.
There are too many instances where Elvis is telling his plan to Dylan but has not turned his microphone off.