The Zodiac Killer was notorious for leaving all manner of clues for police and the media. These ranged from straightforward details of his crimes to plans to construct bombs, to bizarre ramblings. The main source of intrigue in popular culture is the killer’s 340 cipher; one of several symbol-laden letters he left to be decoded. This one stood out in the public imagination as it was not decoded until 2020 (via The Washington Post). Conversely, he seldom left any trace of himself, with none of his scarce fingerprints and DNA leading to anything so far (via Medium).

It obviously served him no practical benefit to write his message on Hartnell’s car, as this was time he could have spent escaping. Nor was it his most flagrant contact with the police, as he (supposedly) called them via a payphone a few months prior. Yet he did it, evidently, because he could. Even after the murders stopped, he continued to send ominous threats, likely for the purpose of reminding police and the public that he was still out there. While far more quiet killers have been caught in recent years, such as the Golden State Killer in 2018, there is no guarantee the Zodiac killer will similarly be brought to justice.