SF Jury Convicts Woman of Murder, Dismemberment of Her Roommate

The apartment at 255 14th Street in San Francisco's Mission District held a grim secret for weeks in the spring of 2018: Margaret Mamer's dismembered remains, stuffed into a blue plastic container in the building's basement storage area. On Wednesday, a jury decided that Mamer's roommate, Lisa Gonzales, put them there.

After nearly eight years, Gonzales, 55, was convicted of second-degree murder in Mamer's killing, and the jury returned a separate true finding that she personally used a knife. She faces 16 years to life in prison. Sentencing is scheduled for April 24 at the San Francisco Hall of Justice, where the judge will weigh prosecutors' recommendation, defense mitigation, and California's mandatory sentencing framework for second-degree murder.

The case turned on a routine landlord-tenant dispute that never went through proper channels. Gonzales, the master tenant who had lived in the 14th Street apartment for decades, gave Mamer 30 days' notice to vacate in mid-April 2018. Mamer, 61, had moved in just the prior year and was paying $400 a month. When coworkers offered Gonzales legal routes to force an eviction, the DA's office said she replied: "No thanks, I'll do it my way."

A third roommate's testimony proved central to the prosecution. That witness told investigators she arrived home on May 15, 2018, to Gonzales warning her away from the bathroom. She later reported hearing sawing noises from inside the apartment. Neighbors independently described foul odors emanating from the building around the same time.

Mamer's friends reported her missing on June 1 after losing contact with her. The next morning, a separate person walked into a San Francisco police station to report that a murder had occurred at the 14th Street address and that a body was hidden in the basement. When officers arrived, Gonzales invited them inside and told them Mamer had relocated to Eureka on May 15. A search of the building's storage area found a blue plastic container with human remains later identified as Mamer's. Crime scene investigators processed the bathroom and found her blood throughout the space. An autopsy concluded she died from multiple sharp force injuries.

District Attorney Brooke Jenkins, who had worked on the case during her earlier tenure in the homicide unit, described the verdict as long-delayed justice. "This is one of the most gruesome crimes our city has experienced in recent history," Jenkins said. She added: "Sadly, not only was she dismembered, but it took a number of weeks to locate her, and so the body had experienced significant decay by then."

The nearly eight-year gap between the 2018 discovery and the 2026 verdict reflects the difficulty of building a murder case without a surviving eyewitness to the killing itself, requiring homicide investigators and forensic teams to piece together physical evidence, the bathroom crime scene, and the third roommate's account. The defense argued the killing lacked the premeditation required for first-degree murder; jurors agreed on that point, convicting on second-degree murder, which requires proof of malice but not planning.

The knife enhancement, found true alongside the murder count, carries its own sentencing weight and narrows the grounds on which Gonzales could seek leniency at the April 24 hearing. Assistant District Attorney Melissa Demetral, who called the case "deeply disturbing and heartbreaking," led the prosecution that delivered a verdict to Mamer's family nearly a decade after her death inside a shared apartment in the Mission.