Clearly, a Trooper MK. III. Look at the trigger, the frame forward of the trigger guard, and the Colt rear sight.
No way it could be a Highway Patrolman. The barrel sticks out too far beyond the extractor rod lug. The four-inch M28 S&W probably doesn't have over half an inch or so of barrel beyond that lug, although I don't have one to measure. Also, the size of the frame is too small.
You can see S&W M28's in, "Telefon" and, "The Mean Season". I may be thinking of the book cover on the latter, which showed a six-inch M28, but one may also be in the film. Long time since I saw it.
Lone Star