The 2018 killing of Margaret Mamer ended with Lisa Gonzales receiving a 31-years-to-life state-prison sentence this summer.
SAN FRANCISCO, Cal. — Long before police searched a Mission District basement or prosecutors took a murder case to trial, another resident of a 14th Street apartment noticed that something inside the home had changed. She was told to stay out of a bathroom, later smelled an unusual odor and then heard sawing sounds from behind the bathroom door for hours. Nearly eight years later, those observations were among the evidence in the case that sent her roommate, Lisa Gonzales, to prison for 31 years to life.
The witness account placed an ordinary housemate in the middle of events that investigators would later connect to the death of Margaret “Maggie” Mamer, 61. Prosecutors said Gonzales killed Mamer in May 2018 after growing conflict over Mamer’s continued presence in the apartment. A jury convicted Gonzales, now 55, of second-degree murder in April 2026 and found that she personally used a knife. Superior Court Judge Teresa Caffese sentenced her Aug. 3, ending the principal court proceedings in a case that had remained unresolved for most of a decade.
According to evidence presented at trial, the other roommate returned to the apartment during a lunch break on May 15, 2018, and Gonzales warned her not to go into the bathroom. When the roommate returned after work, prosecutors said, she noticed a metallic smell inside the residence. She then heard what she described as sawing sounds coming from the bathroom. The sounds continued for about four hours. By the next morning, Gonzales was still in the bathroom, according to the account later given to investigators.
When the roommate came home again, the apartment no longer smelled the same. Prosecutors said she instead detected vinegar and bleach. The bathroom door was open, but another household item was gone: a blue plastic container the roommate normally used to hold dirty clothing. She also noticed a hacksaw beneath a sink in the laundry area. At that point, Mamer was absent. Asked where Mamer had gone, Gonzales said she had left, “but not the way she wanted to,” according to prosecutors.
At the time, the roommate did not have the information police would later assemble. Mamer’s disappearance became a formal concern on June 1, when friends who had not heard from her for several days reported her missing. They already knew there were tensions between Mamer and Gonzales, the district attorney’s office said. On June 2, another person went to police with a far more specific allegation: that Gonzales had killed someone and had attempted to conceal the body in a container in the basement of the building.
San Francisco police officers went to the 200 block of 14th Street and contacted Gonzales. According to prosecutors, she allowed the officers inside and sat with them in the kitchen. Gonzales told police she lived there with one roommate and said Mamer no longer lived in the apartment. She claimed Mamer had moved to Eureka and said she had helped Mamer move on May 15. Police continued looking through the property rather than treating Mamer’s whereabouts as resolved.
Officers searched a storage area connected to the building and found a blue container. Inside were human remains later identified as Mamer’s. Investigators then examined the apartment as a potential crime scene. The police department’s crime scene team found Mamer’s blood throughout the bathroom, prosecutors said, even though bleach had been used in an effort to clean the area. The physical evidence gave investigators a way to compare the bathroom with what the third roommate had described about the period when Mamer vanished.
The medical evidence also established that Mamer’s death was a homicide. An autopsy concluded that she died from multiple sharp-force injuries involving her face, head and chest. Prosecutors said Gonzales dismembered Mamer after killing her as part of an attempt to conceal the crime. The government’s theory was therefore supported by several different categories of evidence: the condition of the bathroom, Mamer’s remains, the other roommate’s observations, Gonzales’ statements about Mamer leaving and the earlier conflict between the two women.
That conflict had developed months before the killing. Mamer began living in the apartment in August 2017, when she and Gonzales agreed on rent of $400 a month, according to earlier court reporting. Gonzales’ public defender said in 2018 that Gonzales had met Mamer through work and had taken her in after Mamer experienced housing problems. Prosecutors and defense counsel later described disputes over rent, missing or broken household items and Mamer’s refusal to move when Gonzales wanted the arrangement to end.
By April 2018, Gonzales had given Mamer a 30-day notice to leave, according to prosecutors. Gonzales also complained about the situation at work. When coworkers described legal ways to remove a tenant, prosecutors said Gonzales rejected their suggestions and replied, “No thanks, I’ll do it my way.” Jurors heard that statement as part of the chronology leading toward Mamer’s death. Prosecutors did not rely on it by itself; the trial also included physical evidence and testimony about what happened before Mamer disappeared and what police found afterward.
The prosecution began in June 2018, shortly after police discovered Mamer’s remains. Gonzales appeared in court that month and eventually entered a not-guilty plea. Her attorney at the time urged the public not to reduce his client to the accusations against her and described her as a hardworking single mother with deep roots in the apartment. Gonzales’ family had occupied the rent-controlled residence for decades, and she had previously fought an attempted eviction there. The defense also said she had not known Mamer particularly well before offering her a room.
The case did not move rapidly to trial. Early proceedings were delayed as lawyers waited for the medical examiner’s work and reviewed discovery, including interviews, forensic material and other evidence. An autopsy report was released publicly in 2019. Gonzales remained in custody while the criminal case continued. By the time jurors heard the case in 2026, almost eight years had passed since Mamer’s friends first reported her missing and officers found her remains in the building.
Jurors ultimately convicted Gonzales of second-degree murder and found true the allegation that she personally used a knife. District Attorney Brooke Jenkins said after the verdict that Mamer’s family and friends remained affected by her death after the lengthy wait for a resolution. Assistant District Attorney Melissa Demetral, who prosecuted the case, called it deeply disturbing and thanked jurors, police investigators and those close to Mamer for staying involved through the long proceedings.
At sentencing four months later, Judge Caffese ordered Gonzales to serve 31 years to life in California state prison. Jenkins said the sentence provided accountability after the extended prosecution. The punishment marked the formal culmination of a case in which seemingly disconnected observations inside a shared apartment — a warning about a bathroom, hours of unusual noise, chemical smells, a missing storage bin and an absent roommate — became pieces of evidence tested before a jury years later.
Prosecutors have announced no additional trial arising from Mamer’s death. Gonzales is now serving the 31-years-to-life sentence imposed Aug. 3. The final judgment leaves the third roommate’s account as an important part of the public record in a case that began inside a shared Mission District home and did not reach a verdict until April 2026.
Author note: Last updated September 20, 2026.