Officers went to the home of Ritchie Lei Lusung Campued, 33, of Vallejo, on Paddlewheel Drive to conduct a welfare check at around 1:20 p.m., according to the Vallejo Police Department.
Police were looking for the woman after receiving a call that she might have been killed by her boyfriend William Ubando, 39, of Vallejo.
Campued's silver Toyota Tacoma was located in a parking lot near tennis courts at Glen Cove Park, police said, covered in what investigators believed was a large amount of blood.
At around 5:25 p.m., a coworker of Ubando contacted police and said the suspect had shown up at his house and allegedly confessed to killing his girlfriend. Ubando also told his coworker the woman's body was in his car.
Officers went to the American Canyon home and arrested Ubando without incident.
A woman's body believed to be Campued's was found on the floorboard of the front passenger seat of the suspect's car, police said.
Ubando was booked into Solano County Jail for kidnapping and murder.