WOODLAND HILLS, Calif. -- Police continued their investigation Friday into a standoff in which five people died, including an LAPD SWAT officer.

After killing three people Thursday, a gunman police identified as Edwin Rivera, 20, shot an officer to death and wounded a second in a gunbattle at a home in Winnetka before he was killed by police in a second shootout hours later, officials said.

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It was the first time that an LAPD SWAT team member was killed on duty since the elite unit was created in 1967.

The violence occurred at a house that was later gutted by a fire that police said apparently was sparked by a "flash bang" diversionary fired into the dwelling by SWAT officers.

"It is a tragedy what happened out there, but it could have been much worse," Los Angeles Police Department Assistant Chief Jim McDonnell said.

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Killed in the shooting was LAPD Officer Randy Simmons, 51, McDonnell said. Simmons was married with two children.

Critically wounded but expected to survive was Officer James Veenstra, the 51-year-old husband of an LAPD captain. Veenstra underwent about three hours of surgery on his jaw, police said.

The two officers have served more than 25 years apiece in the LAPD, more than 20 in the SWAT team, McDonnell said.

Also dead were the gunman and at least three other people, said LAPD Deputy Chief Michel Moore. The victims were related to one another and the gunman, police said. They have been identified as Gerardo Rivera, 54; Edgar Rivera, 21; and 25-year-old Endi Rivera. Gerardo Rivera was the shooter's father, and Edgar Rivera and Endi Rivera were the gunman's brothers, police said.

No other victims were found in the residence, police said.

Veenstra suffered a gunshot wound when a bullet came "crashing into the left side of his lower jaw ... and fragmented into dozens of pieces," said Dr. Gabrial Aslanian, the oralmaxillary trauma surgeon who earlier operated on the officer.

Veenstra will require reconstructive surgeries, but is expected to survive, Aslanian said.

Edwin Rivera was reported to be known to police and had psychological problems.

"We've had some dealings with him," Lt. Tom Smart of the LAPD'S West Valley Division gang unit told the Daily News newspaper. "He's got some gang ties, a rap sheet and some mental health issues."

LAPD Chief William Bratton, who was at an international conference of police chiefs in Canada, made an emergency return to the Southland and conducted a noon briefing with Mayor Antonio Villaraigosa and other officers.

"The caliber of these officers is incredible," Bratton said. "They represent the best of the best."

Bratton said Simmons served as a mentor and peer leader for other officers, and also volunteered to oversee toy drives and other programs for children.

It was the first fatal shooting of an officer in the history of the elite LAPD SWAT team, which was created in 1967 and went on full-time status in 1971.

Funeral services for Simmons will be held on Feb. 15.

Timeline Of Events

The incident began around 9 p.m. Wednesday when a man locked himself inside a home in the 19800 block of Welby Way after calling police to claim that he had killed family members.

Officers went to the location and tried to contact the man. About 12:30 a.m., the officers entered the residence, McDonnell said.

"What we were faced with was a barricaded suspect who had apparently murdered three other individuals," Moore said.

"When the officers first entered the house, they were met with gunfire, but they also found ... three males -- two apparently deceased, a third one possibly still alive," Moore said.

"While the officers were exchanging gunfire with the suspect, and two of our officers were wounded -- one mortally -- a rescue was performed of the third male who was still inside the house. He was taken to the front of the residence ... and unfortunately he was also pronounced dead at the scene."

Video: Timeline

The wounded officers were brought out by their colleagues and were taken to Northridge Medical Center, where Simmons died shortly after 1 a.m. and Veenstra underwent surgery.

Police tried to contact the suspect, employing assistance from members of his family, Moore said.

At about 5 a.m., SWAT officers fired tear gas into the residence, Moore said. At that time, a woman came out of the rear of the residence and was rescued, Moore said.

Officers tried to get the gunman to surrender, to no avail, Moore said. About daybreak, a fire began in the residence, which eventually consumed the home.

Firefighters worked to douse the flames and prevented them from spreading to other homes, Moore said.

Wednesday morning, hours after the first gunbattle, "the suspect again presented himself as a risk and a threat to our officers," Moore said. "A further exchange of gunfire occurred. The suspect went down with injuries. He was later secured and was pronounced dead at the scene."

The last LAPD officer killed in the line of duty was Officer Landon Dorris of the Northeast Station, who was fatally struck on Oct. 22, 2006, in a traffic accident as he was driving to investigate a minor traffic collision.

The last LAPD officer to be fatally shot while on duty was Officer Ricardo Lizarraga of the Newton Station on Feb. 20, 2004. He was shot below his protective vest while investigating a domestic disturbance in the Leimert Park area of Los Angeles.

Police: Shooter Had 'Significant Mental Problems'

Police Friday said Rivera had "significant mental health problems" and had a juvenile criminal record.

Deputy Chief Gary Brennan said Rivera's problems began shortly after the death of his mother when he was ten or eleven, and had become progressively worse.