PLEASANTON — The 34-year-old mystery of how Karen Rose Robinson died has been solved.

Heroin, not a person, killed her.

The clothed body of the 21-year-old Oakland woman was found in a turnout off of Foothill Road in Pleasanton in 1975. Although it was ruled she had died from intravenous drugs and there was no bruising or signs of a struggle, the pathologist could not determine if her death was an accident or if someone had killed her.

The case was classified as a homicide, but no charges were brought. According to a new case summary released by the Alameda County Sheriff's Department, other than a statement from her 28-year-old boyfriend at the time, which investigators thought was questionable, they had nothing to go on

In 1975, the boyfriend told officers he had given her $10 and dropped her off near Oakland City Hall that night, but when deputies talked to him earlier this year, he came changed his story.

According to the case summary, he told them that in 1975 he was selling heroin for Huey Newton out of his Oakland apartment. Robinson, who did use heroin, was with him the night she died. He said without his knowledge, Robinson had taken a more pure form of the drug than she normally used. He said later he found her unconscious.

He told deputies he tried to revive her but she wasn't breathing. The man realized she was dead. He then said he consulted a friend on what to do and was told he would be charged with

Deputies believed his new story

"He felt terrible," said Sgt. Scott Dudek, the cold case unit supervisor. "He loved her. He was given advice from the beginning not to go the police."

The man told investigators he put Robinson's body in a front seat of his car and drove to "Dublin." He took the Santa Rita Road offramp off Interstate 580 and went past the fairgrounds, he said. He left her body near there.

The goal of the his unit, Dudek said, is to solve the agency's cold cases. Not all of them lead to an arrest, he said, but that's all right.

"We can rest this case for everyone involved," Dudek said. "It's as important as arresting people."

Reach Sophia Kazmi at 925-847-2122. Follow her at Twitter.com/sophiakazmi.