When the man known as the Zodiac Killer sent his last letter to the Press, he declared that the killings would stop. His earlier cryptogram-laden messages had said that he was killing in order to gather slaves for the afterlife. True to his word, it does appear that Zodiac did not kill again.

In the decades since, questions have piled up around the legendary serial killer.

Why did he suddenly stop? Is he still alive? Did he want to be caught? Was it really a single person doing all the killings?

There is, of course, the biggest question of all: Who was he?

For years, the name that gets floated most often when discussing the identity of Zodiac is Arthur Leigh Allen. Zodiac enthusiasts are quick to point out that, while there is no definitive proof that Arthur Leigh Allen is not the Zodiac, neither is there proof that he is.

Allen went through lie detector and handwriting tests that did not result in conclusive proof that he was the killer. A DNA sample from Allen was compared to DNA on an envelope sent by Zodiac, and did not match. Authorities do point out that there is no way of knowing if that DNA actually belonged to Zodiac. But neither did it implicate Allen.

Arthur Leigh Allen died in 1992 at the age of 58. This has not stopped more people from chasing that lead, including amateurs who claim to have solved more of the cryptograms Zodiac sent.

Again and again, attempts to link Allen have come up empty.

Now another name is in the mix,

Gary L. Stewart was adopted as a baby. He began a search for his biological parents and was reunited with his mother, only to learn that his biological father was dead. But when he began searching for more information on his father, he kept running into disturbing discoveries.

His father, Earl Van Best Jr, was thought of as an unsavory character by some in his hometown. He had a criminal record. He had abandoned Stewart when he was a baby. But when Stewart obtained letters written by his father, and started handwriting comparisons, he realized that his fathers handwriting matched that of Zodiac.

Stewart is offering his own DNA sample to investigators, hoping that they will confirm what he is already convinced of: his father, Earl Van Best Jr., was the Zodiac Killer.

Stewart just released a book, based on his journals in hunting down his parents, and his discovery of his father’s notorious identity. “The Most Dangerous Animal of All” is selling out in bookstores.

“I’ve had a whole lot of time to think about it,” Stewart says. “I set out to disprove my theory and every rock I overturned just gave me more and more and more evidence, and at one time I just came to the point in my life that there’s nowhere else to turn and nothing else to investigate. My worst nightmare is true, and it is what it is.”

Image via Zodiac Killer Facts