Read the book Zodiac by Robert Graysmith. He makes a plausible case for who it might have been.

I haven't read that one. Was his most likely suspect Arthur Leigh Allen?

From what I've read he seems to be the most likely of all the known suspects.

Russell Johnson Turns Out To Be Zodiac Killer

http://empirenews.net/hollywood-shocker-gilligans-island-star-discovered-to-be-zodiac-killer/

Nobody knows.

There are suspects, that's it.

Major Suspects: Suspects receiving major media and/or law enforcement attention.

Arthur Leigh Allen
Allen is the most popular suspect in the case --most likely due to the publicity given him from two true crime novels. "Zodiac" and "Zodiac Unmasked" detail the evidence and logic pointing author Robert Graysmith's suspect.

Guy Ward Hendrickson
On May 3, 2009, 47-year-old real estate agent Deborah Perez held a press conference in San Francisco, announcing that she believed her stepfather was the Zodiac killer. Perez claims that her stepfather, Guy Ward Hendrickson, took her along on at least two of his attacks in the late 1960s.

Lawrence Kane
Harvey Hines, a retired law enforcement officer, believes that Lawrence Kane is the Zodiac Killer. Kane, who was last known living in Nevada, lived on Eddy Street in San Francisco during the period when the Zodiac killer was active in the Bay area.

Rick Marshall
Rick Marshall was another suspect further developed by former San Francisco Chronicle cartoonist Robert Graysmith.Read more...

Jack Tarrance
(Debunked as a fraud) - Jack Tarrance became a suspect when his stepson, Dennis Kaufman was watching a television profile of the Zodiac Case. Kaufman found many similarities between the Zodiac killer and Jack Tarrance. Tarrance also looked strikingly similar to the composite sketches of the Zodiac Killer.

Robert Tarbox's Suspect
Robert Tarbox purchased a full page ad in the Oct. 17, 2007 edition of the Vallejo Times. Tarbox, 80 years old as of this writing, is a former attorney who once resided in Vallejo, CA.

Bruce Davis
Bruce Davis was a Manson family member convicted in the murders of musician Gary Hinman and former stuntman Donald "Shorty" Shea.

Ted Kaczynski

Mr. X

Michael O'Hare
Gareth Penn's accused Harvard-educated architect Michael O'Hare,a professor at UC Berkeley's Goldman School of Public Policy, of being the Zodiac Killer

Gareth Penn
Gareth Penn was born January 1, 1941 in Carmel, CA is an American author and, in his own words, a "medievalist, artillery surveyor, free lance writer, economic researcher, reference librarian, and receptionist in a robot factory."

"Andy Walker"
William Mentzer

Other Suspects: Less publicized suspects.
Jack Beeman
Joseph Newton Chandler III
The Ohio John Doe.
Mike Kelleher's Suspect
Guy Ward Hendrickson
"Sam"

Confessors: Persons who have "confessed" to being the Zodiac Killer.
Eric Weil
David Martin
An Unidentified San Mateo Man
The Zodiac -A Police Impersonator?