9 Arrested in Slayings at Party in San Marino : Crime: Authorities say suspects are gang members. Police chief fears that witnesses may be afraid to testify.

More than 120 sheriff’s deputies and police fanned out through the San Gabriel Valley on Tuesday to arrest nine alleged gang members in the June 5 slayings of two teen-agers at a high school graduation party in San Marino.

Angered at being asked to leave the party on Lombardy Place after a dispute, gang members returned with semiautomatic weapons and sprayed 30 party-goers with bullets, authorities said. Dennis Buan, 18, of South Pasadena and David Hang, 15, of San Marino were killed and seven others were wounded.

Even as sheriff’s detectives discussed how they overcame the initial reluctance of witnesses to identify the suspects, San Marino Police Chief Frank Wills said he fears that the witnesses may be unwilling to testify in court.

“All the witnesses are absolutely terrified,” Wills said. “But they have strong hearts and souls and they might come around. We’re hoping for a change of heart to go forward.”

Wills added that police hope that other witnesses may yet come forward with information about the seven men and two women.

Those arrested Tuesday were identified by the Sheriff’s Department as Cuong Chanh Phan, 18, of Monterey Park; Hu Tac Chan, 18, of South El Monte; Phuong Tung Nguyen, 19, of Canoga Park; Son That Ton, 19, of El Monte; Thuan Quang, 25, of Garden Grove; Vi Quoc Cha, 18, and Long Huynh, 24, both of Rosemead; Tami Thi Tran, 19, of Westminster, and a 17-year-old Rosemead girl whose name was being withheld because she is a juvenile.

All were charged with two counts of murder and seven counts of attempted murder, said a Sheriff’s Department spokesman.

A source involved in the investigation said that those arrested are mainly ethnic Chinese from Vietnam and belong to a well-established, multiethnic Vietnamese gang. The gang, begun 19 years ago, is believed to be responsible for two slayings earlier this year in the San Gabriel Valley. So far police have not gathered enough evidence to make arrests in those cases.

Deputies, who were assisted by Monterey Park and San Marino police, served search warrants beginning at 7:30 a.m. Tuesday at 11 homes in Pasadena, Rosemead, El Monte, San Gabriel, Monterey Park, South Pasadena, Westminster and Stockton, said Sheriff’s Department Chief of Detectives William Baker.

Authorities recovered five weapons: a 9-millimeter handgun, an AK-47 rifle, two shotguns and a .380-caliber handgun with an interchangeable barrel capable of firing different-caliber ammunition, Baker said.

A white Honda sedan, believed to be a getaway vehicle, was also seized. A 1990 or 1991 Honda Civic was broadsided by a party-goer fleeing the shooting. Baker said the car that deputies recovered Tuesday has body damage.

The shootings shocked the upscale and generally peaceful city, which has a population of 13,000. For the first time in its history, city officials offered a $20,000 reward for information leading to the arrest and conviction of the assailants.

San Marino police said they found themselves grappling with cultural differences in dealing with residents of Asian heritage who make up nearly a third of the city’s population.

Although as many as 15 party-goers witnessed the shooting, few came forward initially with information, Wills said. Detectives said Asian youths told them that they feared reprisals and did not want to be disgraced through association with police or the shooting, even as innocent victims.

Investigators were stymied for more than two months. San Marino police consulted Asian task forces in other cities to help bridge the communication gap.

A break in the case came when sheriff’s detectives from the auto theft task force, who were investigating an unrelated carjacking that occurred before the shootings, discovered information that led to Tuesday’s arrests, Baker said.

The party, given at a posh San Marino house, attracted more than 100 youths, many from out of town, drawn by a flyer that advertised an “End of the Year Jam.” The shootings were sparked by a dispute between the party’s disc jockey and late-arriving gang members, police said.