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.
My point was the posted, open threat of lethal force at supposed UFO sites, which was disputed. In other instances, civilians and military personnel who describe seeing UFOs have had lethal threats from ranking military officers. Ordinary top secret matters do not generate such dire warnings, or the campaign of discredit that Bob Lazar (and others) experienced.