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.
Revealing mistake: When the first scene at Emma's hideaway was shown, obviously the two characters Emma and Jessica were filmed seperately on the couch and then the film was put together (as both are played by Angela Lansbury). However Jessica did a lot of moving while she was talking, so Emma was looking straight across at where she had been, despite her bending down while she talked.
Tinker, Tailor, Liar, Thief - S8-E15
Revealing mistake: In the second close up shot of Nigel Atkins lying dead, after Jessica drops her Harrod's bag in the chair, it is obvious he is still alive as you can see his pulse on the side of his neck.
Deadly Lady - S1-E2
Revealing mistake: When Howard Duff's two daughters enter the police station to identify his body, the cop pulls back the blanket. Howard's eyelids are moving even though he is supposed to be dead.
Revealing mistake: When Cagliostro is stabbed, there's a protruding rectangular pad under his shirt where the knife is stuck.
Revealing mistake: When the episode ends and Jessica drives the buggy, she is replaced by a very obvious stunt double with a wig that not only does not resemble her hairstyle, but it's grey as opposed to her light blonde colour.
Revealing mistake: Kat pumps her shotgun several times with no shells coming out.
Revealing mistake: All the shots of snow falling, mainly when Gunnar is about to be killed, are a very obvious crappy footage of flakes falling projected over the footage of the show. Not a single flake falls on the objects nor the people.
Something Borrowed, Someone Blue - S5-E9
Revealing mistake: When the corpse lies on the bed the pad under the clothes where the thermometer is stuck protrudes.
Trevor Hudson's Legacy - S5-E18
Revealing mistake: There are 2 scenes involving Jessica inside a car. In the first one the car drives calmly as seen from the outside shots, but from the shots inside the car is speeding. When the episode is about to end the car speeds to the police station and now the exact same projection is played, though this time it makes sense.
Revealing mistake: When Jessica is meeting with Congressman Dan Keppner, there are two windows with the Capitol building behind. One can see it's a painted backdrop, most noticeably the window on the left with the garden view.
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.
The Murder of Sherlock Holmes - S1-E1
Revealing mistake: In part 2 of the episode, when Jessica is mugged, Angela Lansbury is replaced with a younger and thinner stunt double twice: when she runs away and when she protects herself against the wall.
Revealing mistake: When Jessica rides on the motorcycle, one can see it's a much younger and thinner stunt double who doesn't resemble Angela Lansbury.
Revealing mistake: After Denton falls off his horse, Jessica arrives and jumps off hers. Her stand-in is a much younger and thinner woman who looks nothing like Angela Lansbury.
Death Takes a Curtain Call - S1-E9
Revealing mistake: When the cops arrive at supper time at Jessica's door, the background is a blatant painted backdrop. (00:31:45)
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