This article contains themes of murder and sexual violence.

Netflix's explosive new documentary This is The Zodiac Speaking reveals previously unknown evidence surrounding the man police have long suspected to be the murderer, Arthur Leigh Allen. Allen's untimely death in 1992, at the age of 58, appeared to put an end to the case, with the killer's identity unsolved. The Zodiac Killer had seven confirmed killings between 1969 and 1974 in the era of serial killers. Still, he is a unique figure in American crime for the letters he sent to police and the media after each killing. The Zodiac Killer's letters contained ciphers full of astrological symbols, which, he insisted, would expose him if solved.

Throughout the 1970s, and until his death, Allen was the police's only named suspect for the Zodiac Killer murders; they connected Allen to the killings through largely circumstantial evidence and a tenuous link to the first victim,...