Visible crew/equipment: As Leary is falling at the end, you can see the safety wire the stuntman is using as he falls backward.
Visible crew/equipment: The boom mic is reflected in the limo's windshield as Clint Eastwood jogs alongside it, after Leary's first phone call.
Chosen answer: The two hunters had now seen his face so they had to be killed. If they reported Booth to the police as "a weirdo in the woods with a powerful gun" (or whatever) his face would become known to the authorities and his chances of getting anywhere near the president would be zero.
The_Iceman