A new book claims that the infamous Zodiac killer is still alive and living in Northern California.

"The Zodiac Killer Cover Up" was written by a former California Highway Patrol officer, Lyndon Lafferty, and adds another theory to the much-discussed serial killer case in Northern California.

The Zodiac killer is blamed for at least five slayings in 1968 and 1969. There was never an arrest in the case.

Three killings occurred in Vallejo. Teenagers David Farraday and Betty Lou Jensen were shot to death in December 1968. Darlene Ferrin, 22, was shot and killed seven months later at Blue Rock Springs Golf Club. Her companion, Michael Mageau, 19, survived.

In "The Zodiac Killer Cover Up," Lafferty claims the killer is now a 91-year-old man living in Solano County. The book uses aliases and does not identify the alleged killer by name. Lafferty claims he and other lawmen investigated the suspect in the early 1970s but were stymied by "power brokers" in Solano County.

According to the San Francisco Chronicle, the book has stirred new debate among those who have followed the famous killings.

The San Francisco police formally closed the case in 2004.