Los Angeles Police Chief William Bratton says there may be an additional victim in the burned house where a gunman, a SWAT officer and three other people were killed overnight.

The standoff began about 9 p.m. Wednesday night in the San Fernando Valley. Nearly six hours later, police lobbed tear gas into the home and hit it repeatedly with a battering ram. Less than 90 minutes later, the house could be seen on fire.

Police exchanged gunfire with the suspect again and he went down. The suspect was taken into custody and pronounced dead on the scene, police said.

"We made every effort to reach out to the suspect," said Deputy Chief Mike Moore, who served as the incident commander during the standoff. "Unfortunately, the suspect had no contact with us and showed no effort to surrender."

Police believe the suspect and the men killed were relatives, but an exact relationship was not known.

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When police entered the house they found two males shot dead and another who was shot but alive. Police brought the wounded man outside and tried to resuscitate him but were unsuccessful.

He was pronounced dead at the scene.

Police said they reached out to other cooperative family members, who also tried to talk with the suspect.

Moore said the suspect was thought to be a risk to other officers.

When tear gas was released into the house, a woman suddenly appeared from the back of the house. Police believe she was there during the earlier shootings.

Police were interviewing her and said they believe she is a victim.

Several blocks of the San Fernando Valley neighborhood were sealed off with yellow crime tape as a police helicopter circled overhead with its searchlight on.

Both officers were taken to Northridge Medical Center, where one of them, 51-year-old Randal Simmons, died just after 1 a.m., Assistant Chief Jim McDonnell said. The other, 51-year-old, James Veenstra, was undergoing surgery and was expected to survive, McDonnell said.

McDonnell said another SWAT officer had undergone successful surgery after being shot in the standoff in the San Fernando Valley.

Mayor Antonio Villaraigosa said he had visited with the family of the slain officer. Simmons leaves a wife and two children. Veenstra's wife is a captain on the force.

"This is a very horrible tragedy and our hearts go out to all the members of the LAPD who also are grieving at this time," Villaraigosa said.

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The Associated Press contributed to this story.