A man already charged with murdering two people last month in San Francisco's Japantown has been accused of committing another killing two months earlier, and police said Wednesday that they were investigating whether he had been targeting Asian American victims at random.

Joseph James Melcher, 25, was charged Tuesday with killing Robert Stanford, 21, who was shot early Aug. 27 as he and a 16-year-old friend drove away from the home of Stanford's girlfriend in the Portola district. The friend was wounded but survived.

Police say that it was nearly two months later, on Oct. 21, when Melcher walked into the Flow bar on Post Street, asked for a woman who turned out not to be there, then opened fire. Song Sun Lee, 34, of San Bruno, was killed.

Melcher then allegedly walked across the street and gunned down Stephen Kam Yan Li, 22, of San Francisco, as Li walked with his girlfriend in the Japantown Plaza.

Police said Melcher had been living in Panorama City in the San Fernando Valley and didn't know any of the victims. The only thing those who were shot appeared to have in common, investigators said, was that they were Asian American.

Lt. John Murphy of the homicide detail said police were looking at whether Melcher, who is white, may have singled out Asians at random. Earlier this month, investigators searched Melcher's former apartment looking for evidence of "antipathy to Asians," court documents show.

But Murphy said investigators have yet to establish a motive in any of the killings.

"There is no way to determine that," Murphy said. "He's not talking.''

Police believe that Melcher, who was raised in the Bay Area, drove up from Southern California in rented cars before the killings in August and October.

He has been held without bail since he was arrested shortly after the Japantown shootings. Police caught him after a short car chase, and said they had found the gun used to kill Lee and Li in Melcher's vehicle.

Ballistics tests on the handgun, a .45-caliber automatic, showed it was the same weapon that killed Stanford, police said.

Stanford was killed just after he left his girlfriend's house on the 2600 block of San Bruno Avenue, where he had spent the evening playing Monopoly. A video from a nearby surveillance camera shows that a bald man stopped his car in front of Stanford's house and, without saying anything, opened fire.

Police say Melcher had rented a red Chevrolet Cobalt, similar to the one used by Stanford's killer, nine days earlier in Los Angeles. The gun that killed Stanford and the Japantown victims was picked up from a dealer in West Hollywood on Aug. 22, police said.

Investigators who searched an apartment earlier this month in Panorama City that Melcher rented about five months ago found the makings of what could have been a pipe bomb, including a fuse, Murphy said.

According to court documents, police were looking for any evidence related to Melcher's motive in the Japantown slayings as well as the Stanford killing, including "antipathy to Asians.'' However, Murphy said the search had not led police toward determining the killer's motive.

Police have also interviewed the woman they believe Melcher may have asked for in the Flow bar the night of the Japantown killings. Investigators say the two knew each other from the time when both attended City College of San Francisco.

"It wasn't like they were boyfriend and girlfriend," Murphy said. "He wanted to be her boyfriend. Her response was, 'Get away from me.' ''

In 2003, Melcher was ordered to attend counseling after he shouted threats at the woman at the City College library that February, records show.

The woman, identified in court records as Jussara Yip, had already obtained a restraining order against Melcher, records show.

In September 2003, Melcher was arrested after hitting a man with a shot glass in a San Carlos pub. Melcher pleaded no contest to misdemeanor battery with serious bodily injury and was ordered to stay away from the victim.

David Garrison, Stanford's stepfather, said the family was gratified that police had made an arrest in the killing. He said the case merits the death penalty, a punishment District Attorney Kamala Harris has promised not to impose.

"I'm mad the city doesn't have the death penalty,'' he said. "If this case isn't deserving of it, what kind of message does that send?''

Melcher has been charged in the Japantown killings with two counts of murder with special circumstances, which would make him eligible for the death penalty or life in prison without parole if convicted. Harris has said her office has not decided what sentence to pursue.