Paul Stine, The Final Known Zodiac Killer Victim

Public DomainPaul Stine’s taxi cab, where he was murdered by the Zodiac Killer.
The last confirmed victim of the Zodiac Killer, 29-year-old Paul Stine, was different from the other known victims. Whereas the Zodiac had previously only targeted couples, Stine was alone when he was killed.
In fact, Stine was working as a cab driver, likely to support himself as he worked toward earning his doctorate at San Francisco State. On Oct. 11, 1969, Stine fatefully picked up the Zodiac Killer as a passenger.
No one knows exactly what happened between them. Stine picked up the Zodiac near Union Square in San Francisco, and took him to Presidio Heights. When they arrived, the Zodiac Killer fatally shot Stine in the head.
Stine’s murder was so different from the other Zodiac Killer victims that investigators didn’t initially tie Stine to the Zodiac. But soon afterward, the Zodiac claimed credit for Stine’s violent death.
Just days after the murder, the Zodiac sent a letter, as well as a piece of Stine’s bloody shirt, to The San Francisco Chronicle.

San Francisco Police DepartmentThe Zodiac Killer, as he may have appeared during the attack on Cecelia Shepard and Bryan Hartnell.
“This is the Zodiac speaking,” the killer wrote in the letter. “I am the murderer of the taxi driver over by Washington & Maple St. […] To prove this here is a blood stained piece of his shirt.”
It seemed like a startling escalation. But even though the Zodiac continued to send letters to local newspapers until the early 1970s, he didn’t kill again.
At least, not officially. The Zodiac Killer ultimately claimed that he had killed as many as 37 people. In a 1974 letter to The San Francisco Chronicle, he wrote: “Me – 37, SFPD – 0.” But that was never proven.
If his claim is true, who could be the Zodiac Killer’s other victims?