The vehicle used on the street is not the same vehicle used for closeups. The first vehicle has a chrome horn ring and plaid seats. The one used for closeups has no horn ring; the seats are a mix of plaid and solid colors.
The first time Sam visits Anita at home he sits on the sofa in front of the trimmed Christmas tree. Later Hilda and the younger sister are trimming the Christmas tree and have a conversation with Mr. Weatherby about how he just bought the tree.
The evening newspaper article says Sam announced the planned chemical analysis that morning, but the clock on the wall when he spoke to the editor indicated it was almost 3 o'clock in the afternoon.
The insurance investigator assumes from the smell of the barrel that various pistols he encounters have been fired recently (a common Hollywood mistake). Once the smoke of a shot dissipates (within minutes), all that even an expert can determine is that a gun has been fired since it was last cleaned --- whenever that might have been --- not how recently it had been fired.
When Sam first calls his boss Blakely about the case, Blakely says he hopes the insurance beneficiary is the killer because then the company won't have to pay off on the policy. That's incorrect. The company won't pay the killer, but the benefits will be paid to an alternate beneficiary or perhaps to the dead man's estate.
When Stu Weatherby and the other man are talking on the stage at the tree lighting ceremony, the microphone easily picks up their casual conversation. But when the sheriff comes to tell them Dr. Gerrow died, the microphone doesn't pick up their conversation even though they are right next to it. Then it easily picks up their voices again when they make the announcement to the crowd of his death.
Anita anxiously checks her watch while waiting for Sam outside the sheriff's office, knowing she must get to Dr. Gerrow's home as soon as possible to return the gun to the collection. When Sam leaves the meeting, he tells her he must go the bank to speak with her father. She drives to Dr. Gerrow's, and, although Sam has no car and must walk there after the meeting at the bank, they both arrive at the doctor's home at virtually the same time. This is especially egregious because it was established in previous dialogue that Gerrow lived in another town five miles south of the city.
When Sam is talking to Anita about the article he planted in the paper, the shadow of the boom mic can be seen to move across his forehead.
When Sam and Larry are leaving Roger's house, the boom mic shadow appears on a porch post as it follows them.
Sam Donovan says the Luger smelled of burnt cordite. Only British cartridges used cordite.
Both the insurance investigator and the sheriff assume that the recovered 9 mm Luger bullet had been fired by a German Luger pistol. In fact, there were several pistols in the 1940s that fired the 9 mm Luger cartridge, among them the Luger pistol, the Browning Hi-Power, and the Walther P-38. Even a ballistics expert couldn't determine the make and model of a pistol merely by glancing at a spent bullet with the naked eye. The cartridge itself has been in production since 1902.
When Sheriff Best enters the front entrance to the Sheriff's office, the sign in front reads "No Parking Police Dept." instead of Sheriff's Dept.