Pasadena Police Chief Phillip Sanchez told reporters that the shooter and his targets appeared to have a landlord-tenant relationship, but did not elaborate.
One of those killed was a neighbour who apparently showed up to help.
After the fatal shootings the 35-year-old male gunman barricaded himself in a nearby house and fired again when a police officer arrived to help one of the victims, Sanchez said.
The shooter then got on the phone, called the 911 emergency number and admitted to his crime. A hostage negotiator was quickly brought in and the shooter was talked into surrendering, the Los Angeles Times reported.
The Times identified the victims as two men and a woman, while a man and a woman suffered minor to moderate injuries.