The 27-year-old was building a life with his longtime girlfriend before a workplace confrontation turned deadly, his family said.
SAN RAFAEL, Calif. — Authorities have identified the man killed during an alleged confrontation with a coworker at Northgate One Shopping Center as 27-year-old San Rafael resident Mathew Ryan Lambdin, as family members remembered him as a man focused on recovery, relationships and plans for the future.
The Marin County Sheriff’s Office Coroner Division released Lambdin’s identity Thursday, three days after he was found critically injured outside a medical office building on Las Gallinas Avenue. Police say Lambdin had been stabbed during a confrontation at a nearby business where he and 20-year-old Justin Amilcar Gutierrez-Navarette worked together.
Lambdin’s family told the San Francisco Chronicle that he had been sober for nearly three years after struggling with addiction and had become deeply committed to his recovery. Relatives and friends described him as devoted to the people close to him and passionate about basketball. He also cared deeply for his dog, Cheeto.
Lambdin had been dating Marisa Phipps for about three years after the two met through recovery, according to the Chronicle. They had discussed building a life together, including moving and starting a family. Lambdin had also been planning to propose, family members said. Their account adds a personal dimension to a case that police initially described only as a fatal dispute between employees.
The stabbing was reported shortly after 1 p.m. Monday. San Rafael police and firefighters responded to the 700 block of Las Gallinas Avenue after receiving a report that a man had fallen and was unconscious. Officers and paramedics found Lambdin with an apparent stab wound as bystanders provided aid. He was taken to a hospital, where he died.
Police said detectives determined from Lambdin’s clothing that he worked at a business within Northgate One. Investigators later concluded that Lambdin and Gutierrez-Navarette had been involved in an ongoing workplace dispute that escalated into a physical confrontation. Police allege Gutierrez-Navarette stabbed Lambdin during that encounter. Authorities have not publicly identified their employer or explained what the earlier dispute involved.
Investigators said Lambdin left through the rear of the business after he was wounded and collapsed outside near the Northgate Medical Dental Center. Shortly after the investigation began, Gutierrez-Navarette contacted police and arranged to surrender, according to the San Rafael Police Department. He was interviewed by detectives and booked into the Marin County Jail on suspicion of murder.
Gutierrez-Navarette remained in custody without bail as of the latest publicly available reports. Police said there were no outstanding suspects. An arrest on suspicion of a crime is not a determination of guilt, and authorities have not announced a final court disposition in the case.
The coroner’s office said the formal cause and manner of Lambdin’s death remain pending the completion of the police and coroner investigations. His family, meanwhile, has focused attention on the life he was building before his death, describing a young man who had worked to overcome earlier struggles and was looking toward marriage and a family of his own.
The investigation remains open, and authorities have not released additional details about the dispute that preceded the fatal confrontation or publicly named the Northgate One business where the two men worked.
Author note: Last updated October 16, 2026.