A private jet at a close by airport took off at about enough time for the shooter to hop on board and escape. It unexplainably disappeared off radar as it crossed into Arizona, then it came back an hour later.

dailymail.co.uk/…/FBI-provo-airport-miles-Charlie…

As for the plant, the old guy they first arrested was claiming he shot Kirk.

sltrib.com/…/george-zinn-what-we-know-about-man/