Continuity mistake: When Ron Moody runs into the sea in pursuit of a suspect trying to escape, he shouts at Jessica to "Get the package!" In the next shot we see Jessica reluctantly follow him in, with a clear waterline from a previous take showing on her dark overcoat/cloak.
Visible crew/equipment: When Trish picks up Jessica at the train station and her car leaves, filming equipment and crew members are reflected in the windows.
Murder of the Month Club - S11-E10
Factual error: When Joellen removes the manuscript from the locker at the Yonkers bus station, you can see the address it was originally mailed too. The zip code is 10205. This is incorrect. All Buffalo, NY zip codes start with "14xxx" a zip code starting with "10xxx" would be much further down state.
Funeral at Fifty-Mile - S1-E22
Other mistake: It's a clear day not a stormy night as it should be when showing the barn in the flashback. Look closely and you can see a clear sky through the barn walls cracks.
Programmed for Murder - S8-E18
Revealing mistake: In the outside shot of the hospital, just before Mort discusses his cough with Doc Hazlet, you can see a sign saying the hospital is located in Ohio, not in Maine. This isn't the only episode where this exact mistake is made.
Murder to a Jazz Beat - S1-E13
Continuity mistake: Jessica and Jonathan sit down to chat; he says, "Tastes and smells... worthy of kings and their consorts," and raises his hands. An instant cut later, from a different angle, they're lowered. (00:04:49)
Funeral at Fifty-Mile - S1-E22
Visible crew/equipment: After Jack's graveside service, Jessica, Mary, and Art walk back to the red pickup, and while they're standing there talking, the mic pops up into view in front of Mary. (00:04:40)
Funeral at Fifty-Mile - S1-E22
Continuity mistake: Carl arrives at the funeral in his RV and then heads to the house. When he arrives, it's a noticeably different model. The door's moved, the front right window is now segmented, and rails have appeared on the roof.
Continuity mistake: When Jessica limps into Milton's car, she holds onto the door. A shot later, her hand is away, and it's Milton's hand instead holding onto the door.
Continuity mistake: When Jessica (a stunt double) is knocked down, her left arm is under her body with her bag in front. An instant cut later (now Angela Lansbury), her arm and bag are behind her back.
Revealing mistake: When Jessica is knocked down by the kids, she is replaced with a younger stunt double.
Continuity mistake: When Milton picks up Jessica at the airport, her bag is hanging over her right shoulder. A shot later, she is holding it with her left hand.
Continuity mistake: The pad where the knife is stabbed protrudes under the writer's shirt.
Revealing mistake: When Miguel tries to sail away, Jessica runs towards the shore. When she enters the water, Angela Lansbury is replaced with a thinner and younger double.
Revealing mistake: When Santana is killed, a rectangular pad where the arrow was stabbed protrudes under his shirt.
Continuity mistake: After Kellijian aims to choke his wife, they kiss. Right afterwards, the position of her left arm on his body is not continuous between shots.
Continuity mistake: Lew Feldman picks up his cigar from the ashtray, but an instant later, it's back on the ashtray.
Continuity mistake: When Patti is shot, Barry kneels down, places his face against hers, and lies on top of her. A shot later, from a different angle, he is away from her, repeating all previous movements.
Continuity mistake: When the robber is killed, his hat falls off. A shot later, it's back on.
Continuity mistake: When Jessica (a stunt double) rides her bicycle at the start, her red scarf is tied around her waist. A shot later, when the real Jessica is shown, the scarf hangs around her neck.
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.