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.
Visible crew/equipment: When Sir John Landry walks towards the fireplace before Jessica unravels the mystery, stage lights are reflected on Jessica's glasses.
Visible crew/equipment: At the beach, when Miguel jumps in the helicopter, two filming lights are reflected on the windows.
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.
Revealing mistake: When Cagliostro is stabbed, there's a protruding rectangular pad under his shirt where the knife is stuck.
Continuity mistake: When Jessica talks to Lt. Bergkamp, she takes her left hand to her ear to improve her hearing, but from the opposite shot, her hand is lowered.
Continuity mistake: Before Joan leaves the restaurant, she has a glass of wine on her right, but from Jessica's POV, the glass has moved to Joan's left side. Also, Jessica's glass is in front of her, but moves to the right side of the table after Joan leaves.
Continuity mistake: When Bud and Andy arrive at Cagliostro's table, Jessica stares with her glasses on, while Joan turns her head around. An instant cut later, Jessica's glasses are off and Joan is turning her head again.
Continuity mistake: When Jessica is having dinner with Joan, Jessica's right arm is either extended on the table next to the cutlery or not, depending on the shot.
Continuity mistake: When Joan leaves the restaurant, her glass is full. Next time we see it, it's empty.
Visible crew/equipment: When Jessica is on her horse at the barn, there's a crew member lying on the floor, watching out for Angela Lansbury.
Death Takes a Curtain Call - S1-E9
Continuity mistake: When Jessica and the Russians escape in the Rolls Royce, the back projection is not continuous between shots. On the right side window, the place swaps between a modern city and a park. On the left window, the same people walking around are played several times.
Visible crew/equipment: When Jessica gets trapped in the car, lighting equipment is reflected on the window.
Continuity mistake: Patti and Brian enter the alley, talk to the card scammer, and keep on walking. From a different angle, they're metres behind, entering the alley again.
Continuity mistake: When Grady introduces the understudy, he puts his arm around her shoulders. A shot later, his arm is away.
Chosen answer: This is the very reason my brother and I used to jokingly call the show, "Murder, She Caused." It's amazing she was ever on anyone's guest list for a party, given the likelihood someone would end up deceased. As to your question, most of the time, Jessica Fletcher would have had an air-tight alibi, as she was in a room full of people, or her whereabouts were accounted for when a murder occurred elsewhere. It also seems to me that there were episodes where she, purely with respect to opportunity, could have been a suspect. I believe she even acknowledged that as a logical possibility from time to time, even though she knew, of course, she was not the killer. However, the investigation would obviously rule out the possibility of her involvement, eventually.
Michael Albert