The whole scenario bugs me though. The plan was to kill the four people and then shoot Sheila through her mouth to make it look like murder and suicide. That could so easily have gone wrong. If Sheila had fought with Jeremy, or if she turned her back, or if she wouldn't let him put the gun against her throat, he couldn't have done anything. I guess he could have planned to sit on her or something, but it would be difficult to control her and position the gun at the same time.