San Bernardino police said they were called to the 1200 block of North Perris Street at about 1:40 p.m. for a welfare check.
Authorities said 42-year-old Julio Serrano went to his brother's home in Los Angeles and told him that he had hurt his girlfriend, 45-year-old Martha Garcia.
Serrano's brother called police and notified them of his brother's statement. When officers responded to the scene in San Bernardino they found Garcia's body inside a trailer parked behind a home.
Serrano was detained by Los Angeles police within hours of Garcia's body being discovered, officials said.
Investigators said the murder appeared to be an act of domestic violence. Serrano was on parole for burglary and numerous prior arrests, and was wearing an ankle tracking device at the time of his arrest, according to police.
Serrano was arrested and booked for murder.
Anyone with information that could aid detectives in their investigation was urged to call Det. Cunningham with the San Bernardino Police Department's Homicide Detail at (909) 384-5745.