Inspector Dave Toschi in 1976. He led the San Francisco Police Department’s investigation into the Zodiac serial killer for nearly a decade, and was portrayed by Mark Ruffalo in a 2007 film. (San Francisco Chronicle via AP)

The letter arrived at the San Francisco Chronicle in April 1978, appearing much like some two-dozen others the paper had received over the previous decade. Its handwriting was slanted, lacking capitalization, and it was signed with a symbol that resembled the crosshairs of a gun.

“This is the Zodiac speaking,” it began. “That city pig toschi is good but I am smarter and better he will get tired then leave me alone. I am waiting for a good movie about me. who will play me.”

The letter puzzled handwriting experts, many of whom said it was a fake, but its target was all too real. For nearly nine years, San Francisco police detective Dave Toschi had led one of the most widely covered murder investigations in American history, searching for a man who called himself the Zodiac and claimed to have killed 37 people.

In fact, authorities said, the Zodiac had fatally shot or stabbed five men and women in the Bay Area and injured two others. The group of victims included two teenagers parked on the outskirts of Vallejo, two teens at a nearby park, a pair of students picnicking in Napa County and a taxi driver, Paul Stine, who became the first and only San Francisco victim when he was shot in the back of the head on Oct. 11, 1969.

His death — the last confirmed Zodiac killing — brought the case to the desk of Mr. Toschi (pronounced TOSS-key), who died Jan. 6 at 86 at his home in San Francisco. The cause was complications from pneumonia, said a daughter, Linda Toschi-Chambers.

At the time of the shooting, Inspector Toschi was perhaps San Francisco’s best-known officer. While other detectives carried themselves with the apparent aim of disappearing from a room, Mr. Toschi donned brightly colored bow ties, smoked plastic-tipped Tiparillo cigars, munched on animal crackers, and carried his gun in an upside-down shoulder holster that had caught the eye of actor Steve McQueen.

The two had met at police headquarters about two years earlier, while McQueen was conducting research for his 1968 cop movie “Bullitt.” Mr. Toschi reportedly served as the model for the movie’s swaggering title character, played by McQueen (the actor ditched Mr. Toschi’s bow ties in favor of a sleek navy turtleneck) and was also credited as an inspiration for Clint Eastwood’s rogue-cop antihero in “Dirty Harry” (1971).

Yet while the fictional Inspector Harry Callahan kicks down doors and tortures suspects in pursuit of a Zodiac-like villain, Mr. Toschi “was by the book, efficient and thorough,” said journalist Duffy Jennings, who covered Mr. Toschi in the 1970s as a crime reporter for the Chronicle.

Mr. Toschi, his partner Bill Armstrong and their law-
enforcement colleagues were never able to pin down the killer, who ridiculed their investigation in cryptic letters that included coded messages and an unrealized threat to “wipe out a school bus some morning.”

Still, his efforts made him a hero to scores of “Zodiologists,” a group of conspiracy theorists and amateur sleuths that includes former Chronicle political cartoonist Robert Graysmith. His research on the subject formed the basis of director David Fincher’s 2007 movie “Zodiac,” which starred Mark Ruffalo as Mr. Toschi.

The real-life detective, who served as a technical adviser on the film, had been off the case for years, reassigned to the department’s pawnshop detail in 1978. He admitted that year to having written anonymous, laudatory letters to the Chronicle, praising his work on the Zodiac case. The letters had been turned over to the police amid suspicion that Mr. Toschi had forged the latest Zodiac letter, which described him as a “city pig.”

The police department “emphatically denied” that Mr. Toschi was ever suspected of forging the Zodiac letter, the Associated Press reported at the time, and Mr. Toschi dismissed the incident as an “ill-advised indulgence,” expressing regret in later years that he had been pulled from the Zodiac case.

“I’m not a vengeful type, but when a life is taken, there must be justice,” he often said, according to Graysmith’s 2002 book, “Zodiac Unmasked.”

“I work with death, sorrow and tragedy,” he continued. “Yet I like my job because it’s a useful one. I bring in killers for society’s judgment. Ringing bells and knocking on doors, good old-fashioned police work. That’s what does it. I’ve even gotten religious-type letters where they tell me to pray, to talk to God, and then I’ll catch Zodiac, they say. These people don’t know they’re talking to the biggest believer around.”

David Ramon Toschi was born in San Francisco on July 11, 1931. His father was a school janitor, and his mother worked at a candy factory. He served in the Army after graduating from high school and saw combat during the Korean War before joining the San Francisco Police Department in 1953.

In addition to the Zodiac case, Mr. Toschi worked on the “Zebra murders” investigation in the mid-1970s, in which a group of Black Muslims were found to have killed 14 whites in racially motivated attacks. According to the Chronicle, he also received a meritorious conduct award from the police department for arresting a man who raped and burglarized senior citizens.

Survivors include his wife of 61 years, the former Carol Bacigalupi of San Francisco; two daughters, Toschi-Chambers of San Francisco and Karen Leight of San Mateo, Calif.; and two granddaughters.

Mr. Toschi retired from the police in 1985 to work in the private-security industry. He told the Chronicle in 2009 that he still visited the site of Stine’s killing, near the intersection of Washington and Cherry streets, on its anniversary each Oct. 11.

“I always park exactly where I parked the radio car that night,” he said. “I look around the intersection, and I wonder what the heck happened. Did we cover all the bases? Did we miss anything at the scene?

“Why didn’t we get this guy? I ended up with a bleeding ulcer over this case. It still haunts me. It always will.”