The Zodiac Killer is an unidentified serial killer who operated in northern California during the late 1960s and early 1970s. The killer is known for committing at least five murders between 1968 and 1969, although he claimed to have killed more. The Zodiac's identity remains unknown, despite numerous investigations by police and the FBI. The killer taunted authorities with cryptic letters and ciphers sent to local newspapers, in which he claimed responsibility for the murders and threatened further violence. His symbol, a cross-circle, became infamous. The Zodiac's last confirmed crime was in 1969, and no conclusive evidence has ever linked a suspect to the killings. The case remains one of the most famous unsolved mysteries in criminal history.