The proliferation of projection technology and electrical gadgets in the 1920s allowed people to conjure spirits. Well, spirits of a mechanical variety anyway. These ghoulish Jazz Age illusions entertained audiences and fooled ardent believers. But some thought that maybe this wave of high-tech ghosts could be put to use beyond the parlor tricks of supposed mystics.
The November 1924 issue of Science and Invention magazine proposed using a slide projector and a little smoke to coax a confession out of alleged murderers—a "novel third degree method," as they put it.
From the magazine:
While the prisoner is asleep, or partly asleep, a picture of the deceased (if the prisoner is a murderer), is thrown on to the wall of a cell. A suitable voice is made to ask some question, such as, "Why did you do it?" A dictaphone is concealed in the wall of the cell, which carefully records any sound that the prisoner may make, while detectives watch his actions.
New recording technology also got in on the act, as a microphone disguised to look like a rock was placed in the prisoner's cell. Once the alleged murderer confessed to the projected ghostly image, it would all be recorded by detectives in the next room. There's no evidence that police departments ever actually tried such a scheme. But, given how far we've come from the projectors of the 1920s, it's not too difficult to imagine some high-tech 21st-century version of this being tried out somewhere in the world with a superstitious inmate.