Blooper

The first murder that Louis Mazzini commits involves him swimming fully dressed underwater to release a boat from its moorings. In spite of having brought no change of clothes or even a towel, he is shown shortly after committing the murder paddling down the river with his clothes bone-dry.

When "The Hangman" (Miles Malleson) opens the peep hole to the prisoner's cell, he moves the covering to the right, with a finger. After we are allowed to gaze at the back of the prisoner's neck for a few seconds, the shot reverts to the outside of the cell door; The Hangman releases the cover which closes from left to right, not right to left, as it should have done.

When Dennis Price is posing as the Bishop of Matabeleland, he says that he speaks Matabele and demonstrates, with a mixture of gibberish and grunts. There is no such language as Matabele. The Matabele at the time spoke a language known as Ndebele.

When Louis is crossing out the twins on the family tree, a rubbed-out cross from an earlier take is visible.

Shortly after we see a notice of the scheduled hanging, dated 1908, the hangman remarks, "Even my lamented master, the great Mr Berry himself, never had the privilege of hanging a duke." He presumably means James Berry who died in 1913.