Character mistake: When the corpse is taken out of the water, he moves his mouth.
Factual error: Celestial navigation can determine one's position on the earth's surface to within about one mile, not precise enough to give the location of a buried treasure. It also requires more than a sextant. It requires tables published in a nautical almanac (which is updated each year), charts on which to plot lines of position, and an accurate chronometer that is set to the precise time at the Prime Meridian (Greenwich Mean Time).
Factual error: "Witches" were burned at the stake in Europe, but not in America. In America, they were hanged.
Continuity mistake: When the episode begins, Jessica is having a meeting with Sally Wilson, who hangs a bag over her shoulder. A shot later, her bag is down and she is hanging it again.
Audio problem: When Buck walks to the bar downstairs and meets Mrs. Oates, the sound of their footsteps is that of tiled floor, but they're walking on a rug.
Revealing mistake: Kat pumps her shotgun several times with no shells coming out.
Mirror, Mirror, On the Wall (2) - S5-E22
Other mistake: When the sheriff finds the apple, the bitten side has a fresh white colour, instead of the brown colour it should have after the many hours passed.
Mirror, Mirror, On the Wall (2) - S5-E22
Continuity mistake: When Eudora arrives at Jessica's home to apologise, she's wearing a pair of gloves. A shot later, the gloves have vanished.
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.
Crossed Up - S3-E13
Continuity mistake: When the crime is solved Jessica shows her emergency calling button. The way she holds it changes between shots.
Crossed Up - S3-E13
Continuity mistake: When Grady grabs the diary it swaps between closed or open depending on the angle.
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.
Something Borrowed, Someone Blue - S5-E9
Audio problem: Whenever someone is walking on a rug the sound we hear is of footsteps on a tiled floor.
Something Borrowed, Someone Blue - S5-E9
Continuity mistake: In the kitchen the police officer loosens his tie, but from the side shot it's still tight.
Night of the Headless Horseman - S3-E11
Continuity mistake: In the car, when Jessica is told that she has to act like Dorian's mother she covers her face with both hands. A shot later there's just one hand on her face.
The Bottom Line Is Murder - S3-E15
Continuity mistake: When the cop picks up the dirty ashtray he blows the ash away. In the close-up the ashtray is spotless as if it had been wiped with a cloth or if it were brand-new. First of all, no ash blew away, and second of all, a mere puff couldn't have cleaned it the way it looks.
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.
Factual error: The whole episode is run as if based in the UK, and yet the script has obviously been written by an American. The UK does not have autopsies, it has post-mortems. The UK does not have a trunk (of a car) it has a boot.
Plot hole: When Jessica is arrested for the murder of the enemy agent. Her purse is confiscated. It was reported stolen by Michael Haggerty. But throughout the whole show none of the cops looked at her ID. Besides that she's a famous women and someone at the police station would definitely know who she is.
Murder Among Friends - S12-E16
Plot hole: End of the show when Diane confesses makes no sense. There were 3 sets of fingerprints on the computer. She killed her with it, but somehow her fingerprints never showed up on the laptop. (00:41:45)
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.