SAN FRANCISCO -- A man, who witnesses say may have been acting as an armed vigilante trying to clean up his crime-ridden neighborhood, was arrested Monday after a shooting and an intense search of a downtown San Francisco apartment building.

Capt. James Drury would not comment on whether or not the shooting was an act of vigilantism.

"They (witnesses) thought he was acting as some sort of official," he told KTVU.

San Francisco police Sgt. Steve Mannina said a witness first called police at 11:53 a.m. to report hearing one gunshot in the 900 block of Post Street. When police arrived in force from a nearby demonstration, they found one victim suffering from a non-life-threatening gunshot wound.

"The suspect allegedly approached a man sitting on a stoop," Drury said. "There were some words exchanged. He (the gunman) made a gesture to his waistband. He pulled out a gun and fired a shot at the victim….Witnesses said he then ran across the street into a building."

The victim was taken to San Francisco General Hospital with a non-life threatening wound to the shoulder, Drury said.

Heavily armed officers quickly swarmed into the building. After a search of nearly two hours, officials located the suspect and a small cache of handguns. He was arrested without incident.

Drury said the alleged gunman was also being looked at as a suspect in a shooting in the same neighborhood on Sunday. He did not know if anyone was wounded in that shooting.