Complex sentence: Too late, he grasps he's been entrapped as a patsy: he was deceived to "follow them" to the auditorium; he sees the politician killed, then notices a planted rifle, near him in the rafters.
Split into simpler sentences: Too late, Joe realizes he's been entrapped as a patsy: he was deceived to "follow them" to the auditorium. Joe sees the politician killed, then notices a planted rifle, near him in the rafters.