Revealing mistake: All of the exterior shots of Jessica and Hagarty are wide shots with very obvious stand-ins. Jessica is thinner and younger, while short-haired Hagarty's double is younger, chubbier, and has long hair around the nape.
Jack & Bill - S6-E5
Revealing mistake: When the episode ends and Bill leans down for the dog to lick him, a shiny light-brown spot is visible on the actor's jaw - seemingly a bit of food placed there to prompt the dog's trained reaction.
Jack & Bill - S6-E5
Revealing mistake: In the toilet scene, when Max slams the terrorist against the wall, he is replaced by a very obvious stunt double with longer hair and a noticeably larger build.
Town Father - S6-E11
Revealing mistake: When the two men knock on Jessica's door to inform her about the murder, the landscape behind them is a painted backdrop.
Revealing mistake: When Danny recounts crashing the pickup and breaking the tail light, you can hear the light shatter when he hits the tree - but it doesn't actually break. In the next shot, however, the tail light is suddenly smashed.
How To Make a Killing Without Really Trying - S6-E14
Revealing mistake: When Jessica enters Gordon Tully's office and looks around, there's a photo of him with Buddy Black. The picture is an awful, poorly done composite: the lighting on their heads doesn't match the rest of the image, the head sizes are out of proportion with the bodies, and the overall light direction is inconsistent.
Revealing mistake: When Bill is stabbed, the pad beneath his shirt - where the knife is stabbed - protrudes.
Answer: In a flashback scene, it was shown that he had a violent temper, so it stands to reason that he finally killed her in a fit of rage.