As mafia queen Dung Ha lazed in front of her modest hotel, sharing a midnight beer with several other women, the hit man suddenly appeared from the dark. He pulled a pistol and shot her in the head. Then he slipped back into the shadows.

Dung Ha had graduated to Ho Chi Minh City from the mean streets of Haiphong, a gritty northern port notorious for smuggling where she had run the local gangs. She had been bent on the big time, on forging an alliance with the Ho Chi Minh City godfather, Nam Cam. But they soon clashed over turf.

Her October 2000 gangland-style execution in a neighborhood popular with foreign backpackers was remarkable in a country where public gunplay is rare. The hit was traced back to Nam Cam, and Vietnamese authorities began to move against the mob boss, ending his generation-long reign and unraveling an extensive criminal network that reached to the upper echelons of the ruling Communist Party.

The investigation culminated in an unprecedented trial that opened here last week. Vowing to root out corruption, Vietnamese officials have charged Nam Cam with murder, gambling and bribery along with 154 others accused of promoting or sheltering a vast enterprise of illegal casinos, cockfighting, drug dealing, prostitution, extortion and sleazy karaoke joints.

It is the largest trial in Vietnam's history, overflowing the freshly painted main courtroom into two other halls where row after row of defendants in green-and-white-striped prison pajamas, guarded by scores of police, watch the proceedings on closed-circuit television.

The place of honor, a center-aisle seat on the front wooden bench facing the chief judge, has been accorded to Truong Van Cam, 56, universally known by his nickname, Nam Cam. As the charges were read -- it took 55 minutes -- he stood with head bowed, occasionally looking up and blinking, hands dangling by his sides. Unlike other defendants who stood stiffly in place, he kept fidgeting, seeming more restless than anxious, though conviction could bring a death sentence.

His alleged co-conspirators include 13 police officials, three prosecutors and three journalists accused of being on his payroll. Also facing prosecution are Vietnam's former deputy security minister, its deputy national prosecutor and the head of the state-owned broadcasting company. The latter two, already ousted as members of the Communist Party's Central Committee, are accused of carrying out a plot involving hundreds of thousands of dollars in bribes to win Nam Cam's early release in 1997 after a gambling conviction.

Normally known for policing its internal affairs behind closed doors, the government directed that the opening day of the trial be broadcast on national television. Authorities also switched on loudspeakers mounted on the chipped ocher facade of the gracious French colonial courthouse so that hundreds of people crowding outside behind police barriers could follow the proceedings.

"The government is televising the start of the trial because it's important to show they are seriously trying to eliminate corruption. They need to win the public's confidence," said Van, an office worker.

Graft remains rampant in daily life -- Vietnamese must pay off crooked cops at traffic stops, crooked doctors for prescriptions and crooked teachers to look after children during the school day -- and has emerged as the greatest threat to the legitimacy of the Communist Party, according to diplomats and foreign businessmen.

"The public trial reflects deep worry about what pervasive corruption can do to the system," said a Western official. "They know it's an explosive issue among the population."

Vietnamese officials have been reluctant to publicly discuss the Nam Cam case but provided latitude for the typically timid press to publish and at times investigate the sensational details.

According to these accounts, Nam Cam began his criminal career at a young age, and was sentenced to three years in prison for murder when he was 15. After his release, he served in the South Vietnamese army and worked the docks of Saigon but continued to build his underworld fiefdom, uninterrupted even by the Communists' conquest of his city in 1975.

In recent years, he ran his operations out of the seedy pink Tan Hai Ha discotheque and karaoke club, where customers could allegedly satisfy their appetites for gambling, ecstasy pills and child prostitutes.

He also expanded into new frontiers, fixing soccer matches and muscling in on legitimate businesses. He considered forays into Hong Kong and Macau and explored links with Vietnamese gangs in the western United States, diplomats said.

But when he and Dung Ha, the Haiphong mafia boss, tried to forge an alliance, the two clashed. The ill-fated, ultimately fatal enterprise left a woman scorned.

In an act of spite that still has Ho Chi Minh City buzzing more than two years later, Dung Ha plotted to surprise Nam Cam as he hosted a birthday party for one of his henchmen at the popular Spaceship nightclub, a concrete discotheque shaped like a flying saucer. She arranged to suspend a large container from the ceiling, promising it would release balloons and other party favors. But when the container was flung open, it showered the guests with rats covered in excrement.

Mortified, Nam Cam gave the order to rub out his rival, prosecutors allege. A month later, she was dead on the sidewalk.

The bloodletting did not end there. In August 2001, one of Nam Cam's lieutenants was killed, allegedly at the direction of a Taiwanese criminal who had been Dung Ha's business partner.

When Vietnamese officials finally resolved to move against Nam Cam, they recognized that the local police department was utterly compromised. Security forces from outside the city were brought in, and Nam Cam was arrested in December 2001 at his mistress's home.

The hero of this tale, as told in the Vietnamese media, is the chief police investigator, Maj. Gen. Nguyen Viet Thanh. Brought in from a southern province, he has been depicted as an incorruptible crime-buster who eschews drink, girls and fancy cars, preferring to dash around on his old Honda motorbike. Thanh's wife continues to toil in the family rice paddy in the Mekong Delta and at times still prepares his favorite dish, traditional fish in a clay pot, and brings it to him in Ho Chi Minh City.

But foreign observers and Vietnamese disagree whether the colossal court proceedings are a showcase for a serious anti-corruption campaign or merely a show trial.

John Shrimpton, director of the Dragon Capital Group Ltd. investment firm, said the government's "root-and-branch" strategy demonstrates its sincerity. "We definitely see a sea change in the authority's approach. They are tackling head-on some of the thorniest corruption issues that three years ago would have been dealt with in a quieter, more low-profile manner," he said.

The government has announced it is also preparing to prosecute two former deputy agriculture ministers on charges of embezzling millions of dollars. And police are trumpeting a tax-evasion probe of prominent businessmen involved in importing mobile telephones.

Yet many in Vietnam doubt the Nam Cam case heralds an effort to purge corruption from the Communist Party itself. "They had to prosecute this scandal once it came out that such high-level people were involved," said Cuc, a businesswoman. "But I don't think they'll do it again. Next time, they'll try to cover it up or clean house quietly if they have to."

"Nam Cam just went overboard," said a Western lawyer. "People know everything is corrupt and they don't expect this case to change anything."

Indeed, even before the trial opened, Vietnamese news reports said a new generation of Ho Chi Minh City mobsters with such names as Dat Long Hair, Nam Fire, Xuan Leprosy and Tuan Malaria have begun skirmishing over the spoils of Nam Cam's casino empire.

Nam Cam, left, the accused crime boss of Ho Chi Minh City, is surrounded by guards and other defendants during the televised opening of Vietnam's biggest corruption trial.