Dire threats against UFO witnesses are well-established. A famous sign at Area 51 even warns that “DEADLY FORCE IS AUTHORIZED.” During the Cold War, the local airport near where I lived also had a major SAC base with U-2s, B-52s, and nuclear bomb storage bunkers. The warning signs against entry there were much less menacing.
Those are not threats to UFO witnesses. It’s a general warning against trespassing in a classified area. We’re discussing those BS stories about mysterious Men in Black. Did anyone threaten Bob Lazar? He sure didn’t shut up.