Sgt. Debra Barry said 58-year-old Leonard Smith was found dead in his home on Drake Avenue around 5 p.m.
It is believed Smith died Saturday afternoon after an altercation with another Marin City resident, Barry said.
The sheriff's office is withholding the name of the suspect as the investigation continues, Barry said.
Investigators attended a memorial service for Smith in Marin City Monday night, Barry said. Marin City community leaders and Smith's family pleaded for witnesses to come forward and cooperate with the investigation, Barry said.
Anyone with information is asked to contact the sheriff's office investigations unit at (415) 499-7265.