Something that's perfectly legal if the government does it. They call it a 'stake out'.
It's perfectly legal if a civilian does it on his own property too, as long as it is not part of a premeditated murder.
If he had made all those extensive preparations, called 911 as soon as he saw them on his CCTV, and held them at gunpoint until the police arrived, he'd be a hero.
But his goal wasn't to catch them.
In his 30 years as a State Department security officer one wonders how many times he got to shoot intruders or just had to detain them to his dismay.
He probably couldn't wait to retire so he could shoot those who dared breach his security perimeter.