The sequence is basically - get to required dialogue stage, Parker gets the "CaptainParkerArrestKeith" package which is a dialogue package. The result is him going to Keith's location and starting a dialogue. When this dialogue completes, he gets the "CaptainParkerKillKeith" package, which is a simple always hit/no damage UseWeapon with a corresponding OnHit by Parker - advance quest/die section in Keith's script.
The problem is, despite the UseWeapon package looking completely fine to my inexpert eye, the weapon never fires - Parker takes aim at Keith, but never fires, and will stay in this aiming pose until the player does something that causes the ai to reset (leave the location, save and reload, etc.)
Anyone have any ideas? I've been mulling this one over for a few days and it has me stumped.