The Allegheny County district attorney's office and Pittsburgh police are investigating Thursday's fatal shooting of a gunman after a nine-hour standoff in North Point Breeze.

Such investigations are routine whenever a police officer is involved in a shooting.

"It will be a thorough review," Assistant Chief William Bochter said yesterday. "It could take a long time."

Around noon Thursday, a SWAT marksman fired a single fatal shot at Lamar Smith, 29, as police rushed an apartment in the 200 block of North Homewood Avenue, where he had barricaded himself since 2 a.m.

Pittsburgh police Chief Nate Harper has described the shooting as justifiable because Mr. Smith moved toward officers with guns in both hands.

Now Chief Harper will make at least three appointments to a critical incident review board that will have the task of going over the day's events.

The district attorney's office had its own investigators at the scene and will conduct its own review, according to Mike Manko, a spokesman for the office.

"We'll be awaiting reports from the city police in order to take a deeper look at what happened," Mr. Manko said. "This is our standard response."

The standoff stemmed from an early-morning argument among Mr. Smith, his girlfriend and her father, who called police.

Officers saw Mr. Smith in the apartment building, clad only in boxer shorts and holding a gun in each hand. He ignored orders to drop the weapons and ran upstairs. Police then called in the SWAT team and negotiators.

Over the next nine hours, Mr. Smith played loud music on his stereo, yelled that he wouldn't be taken alive and tried to escape through a window. He also fired several shots.

Police initially launched tear gas and "beanbag" rounds into the apartment, and they tried to persuade Mr. Smith to surrender. They also deployed a robot.

They went into the apartment when Mr. Smith stopped communicating.

Chief Bochter declined to discuss specific tactics used by the SWAT team, to avoid compromising future operations.

"The point is to end the standoff," he said. "It's training, experience, protocol. It all comes into play."

The city's SWAT team was deployed 87 times in 2008, including 12 standoff situations. None involved the taking of hostages.

"The suspect is the one who dictates the action," said Stuart Meyers, a former SWAT specialist with police in Montgomery County, Md. "If he puts his gun down and comes out, the situation is over."

Mr. Meyers is chief executive officer of OpTac International, a nonprofit organization that offers law enforcement training and this weekend is hosting the three-day National SWAT/Sniper Symposium in Reston, Va.

He said the use of tear gas isn't always effective because the chemicals can seep through open spaces in the room or building holding a barricaded suspect.

Also, Mr. Meyers said, police make their decision to storm a building after considering a range of factors that differ in every standoff.

"If they believe a suspect is getting ready to fire or take some aggressive action, and there's no communication or negotiating," he said, "that could be the opportune time to go in."