A sly stab at the true-crime genre, Charlie Shackleton’s film is like looking at one of those chalk outlines which cops once used to mark out dead bodies. Except in the space where the corpse should be is a movie that never was. Originally, Shackleton planned a documentary based on the book The Zodiac Killer Cover-Up: The Silenced Badge by Lyndon E Lafferty, a cop who seemingly came into contact with the serial murderer who stalked the San Francisco Bay Area in the 1970s. When the family of Lafferty (who died in 2016) refused to grant the rights, Shackleton abandoned his project.

Yet having scouted locations, he refused to let it go; and so here he crafts a mock-doc of sorts, visiting the spots where he would have filmed and explaining to the viewer with droll voiceover just how the film might have looked. One particularly clever moment sees him conjure up a credits sequence, lampooning the all-too-familiar opening reels used by the streamers for their generic true-crime docs. Shackleton examines our thirst for grisly murders, and, if nothing else, it’ll pique your interest in the unsolved Zodiac case.

Zodiac Killer Project, Filmhouse, 15 August, 1.30pm, 17 August, 12.30pm; Vue, 15 August, 9.15pm, 16 August, 9pm.