Man convicted for second time in Potrero Hill murder case

More than 30 years have passed since Barbara Martz was slain in her Potrero Hill home, but on Thursday a jury convicted a San Francisco man of her rape and murder for the second time.

John Davis, 49, was found guilty of first-degree murder with special circumstances this week, according to the District Attorney’s Office. Davis was first convicted of her murder in 2007, but the decision was overturned two years ago because of juror misconduct during deliberations.

This time, the jury deliberated for one day before finding him guilty of murder during the course of a rape and burglary.

“If you commit a heinous crime in San Francisco we will do everything ethically possible to bring you to justice,” District Attorney George Gascon said in a statement. “Justice may be delayed, but it won’t be denied.”

Martz, 28, was raped and “brutally stabbed to death” when she returned home from the grocery store on the evening of Dec. 4, 1985, prosecutors said. Davis, 18 years old at the time, lived one block away from her but was not immediately considered a suspect.
The medical examiner’s office later took samples of semen from her body and stored them in the freezer, according to the district attorney’s office. In 2002, investigators developed a DNA profile from the samples that linked to Davis, who was serving a stint at Pelican Bay State Prison for robbery.

“Thanks to science and the law we were able to bring justice to this family,” prosecutor Andrew Ganz, an assistant district attorney, said in the press release. “Being able to hold this defendant responsible after so many years is an extremely rewarding experience.”

The case was the first time DNA helped San Francisco police solve a violent crime with no known suspect, police said when Davis was first charged.

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