Goofs

When Paula finds the letter in her aunt's music score, Gregory crumples up the letter and jams it into his pocket. Later, when she finds the letter in Gregory's desk, it's neatly folded, with no evidence of crumpling.

Gregory is shown leaving the house from the inside, opening the door most of the way. The following shot, showing the next moment outside, repeats most of the door-opening.

When Brian Cameron confronts Gregory Anton, Cameron is holding Alice Alquist's costume dress. When Anton tries to step away Cameron blocks him and throws it on the floor. However, after Cameron wrestles Anton's gun to the floor, on the following wide shots the gun is visible but the costume dress, which would have been in the same area, has now disappeared.

When Nancy is following Elizabeth up the stairs, they are both carrying several folded sheets. Immediately when they reach the top of the landing the camera focuses close-up on Nancy, who is looking at the closed-off top floor. In this shot she is not carrying the sheets.

The gasolier in the foyer at the beginning of the movie is not the same one in the later scenes.

The guide in the Tower of London is incorrectly shown as wearing the uniform of the Chelsea pensioners instead of the Yeoman guard.

When Gregory has searched the upstairs room for the final time, he has (ostensibly) turned off the gaslight and is climbing to the skylight whereupon he spots the jewel and goes to look. When he lifts the dress to show all of the jewels, the scene is very brightly lit even though the only source of light would be the moonlight showing through the skylight.

(at around 21 mins) When Gregory first plays the pianoforte the instrument is in tune despite it being in a deserted house for many years, and despite Paula's mentioning it would need to be tuned only moments before.

(at around 1h 32 mins) As Gregory searches the clothing in the attic, a camera shutter can be heard.

At the beginning, a man is lighting outdoor gaslights on tall poles, using a long pole with a flame on the end. He is shown lighting one light, then a close-up of the next one shows the end of the pole entering the gaslight glass enclosure, but it has no flame for starting the light. That shot ends before the starter pole lights the light.

After the shot is fired, the maid runs to the door and calls across the street to the policeman. Nancy (Lansbury), who is standing with the policeman, obviously yells out, but there is no sound of her voice heard.

At about 43 minutes in, a man and a woman with an organ grinder walk past Gregory and Paula's house; as the camera begins to crane up, the film crew is reflected in a window.