LOS ANGELES, CA (Catholic Online) - Lyndon Lafferty, a childhood friend of the police's main suspect penned a book on his decades-long hunt for the Zodiac called "The Zodiac Killer Cover-Up" in which he adds an intriguing theory as to who the killer is and why he was never caught.

Lafferty believes that the killer is a 91-year-old man living in Solano County, California, and that he was protected by "power brokers" that refused to stop him.

"Official corruption and political intervention forced the investigation into a top-secret, covert status, giving the insane Zodiac killer immunity and a license to kill," Lafferty declared in his book, published earlier this year.

In the years since the Zodiac's killing spree, law enforcement officials followed dozens of clues that all went cold.

In the letters he mailed to newspapers, he claimed that he killed 37 people.

"The police shall never catch me, because I have been too clever for them," the Zodiac wrote in a letter sent to the San Francisco Chronicle.

His young victims were either stabbed or shot to death in Northern California, All were between the ages of 16 and 29.

The San Francisco Police Department closed the case in 2004, but reopened it in 2007.

While numerous people have claimed they have identified the killer, but none have ever been confirmed by the police department.

The chief suspect in the case, Arthur Leigh Allen, was cleared after DNA evidence taken from the saliva of the Zodiac's sealed letters exonerated him.

Lafferty, who went to High School with Allen, claims that the identity of the Zodiac killer has been known since March 15, 1971.

The motive for the killings, Lafferty says, was adultery.

"Mind and body ravaged by years of severe alcoholism, his blood-lusting revenge turned him into the most shocking and vicious killer in our 20th century," Lafferty writes.

"Through his tauntings of the police, his codes, ciphers, and letters, he was on a mission to redeem his shattered ego, to prove that he is better, smarter, and more clever than all the judges and police put together."

The Zodiac allegedly started his killing spree after his wife had an affair with a Solano County Superior Court Judge.

Lafferty locked onto the Zodiac case in 1970 when he became suspicious of a man he saw parking at Vallejo highway rest stops, according to the San Francisco Chronicle. Lafferty tracked the man, who drove a white Chevrolet sedan and looked just like the wanted posters, and decided he had to be the one.

Lafferty said he even confronted the killer.

"I looked into a quivering, snarling face like I was looking to the face of death," Lafferty said to the Daily Republic. "It scared the hell out of me."

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