SAN FRANCISCO: A dapper former San Francisco gang leader who presented himself as a reformed criminal was the focus of a lengthy organised crime investigation in Chinatown that ended up snaring a corrupt California senator and more than two dozen others.

With opening statements in Raymond "Shrimp Boy" Chow's case scheduled Monday, prosecutors finally will get their chance to convict him of racketeering, murder and money laundering charges that could put him away for life.

A conviction would all but close out a colorful case featuring an undercover FBI agent who posed as a member of the mafia and plied his targets in Chinatown — the heart of one of San Francisco's most popular tourist attractions — with fancy meals, liquor and cash.

Chow's attorneys, led by veteran San Francisco lawyer Tony Serra, plan to make the trial a referendum on the multi-year government probe they say was a costly fishing expedition that induced innocent people into crime.

"History will show that this prosecution was the most shocking of all time," Curtis Briggs, another Chow attorney, wrote in a court filing Wednesday seeking to dismiss the case for "outrageous government conduct." ''The FBI attacked democracy, the right to vote, the people's voice, and spat in the eye of the legislature."

But legal observers say the racketeering conviction of state Sen. Leland Yee in July has largely validated the government's probe and lowered the stakes for prosecutors in Chow's trial.

"The government has gotten what it wanted to get out of this investigation by already putting down Leland Yee," said Peter Keane, a professor at Golden Gate University School of Law in San Francisco and a former public defender. "He was their trophy."

The investigation also sent a message to other politicians and Chinatown power brokers, said Rory Little, a law professor at the University of California, Hastings and a former federal prosecutor.

"'Even Chinatown can be penetrated by government investigations, so stay on the up and up,'" he said. "'And if you're a state senator, don't assume you're safe.'"

Federal investigators say Chow took over the Chinese fraternal group, the Ghee Kung Tong, in 2006 after having its previous leader, Allen Leung, murdered and ran a racketeering enterprise that engaged in drug trafficking, money laundering and the sale of stolen cigarettes and alcohol.

The murder charge was filed last month and made Chow eligible for the death penalty, though prosecutors later said they wouldn't seek a death sentence.

Chow is also accused of soliciting the murder of Jim Tat Kong, a suspected organized crime figure.

Prosecutors will likely point to Chow's criminal history. Chow pleaded guilty to racketeering in 2000 for crimes including heroin and cocaine trafficking, attempted murder and robbery, according to an FBI affidavit in Chow's current case.

He was sentenced to more than 13 years in prison, but served a much shorter sentence after agreeing to testify in another prosecution.

Chow has acknowledged his criminal past, but maintained he went straight after his release from prison.

Federal agents say one of Chow's associates was Keith Jackson, a former San Francisco school board president and well-known political consultant who raised money for Yee's unsuccessful mayoral run in 2011 and bid for secretary of state.

Jackson led investigators to Yee, who acknowledged as part of his plea deal that he accepted thousands of dollars in exchange for favors and discussed helping an undercover FBI agent buy automatic weapons from the Philippines.

Yee is scheduled to be sentenced in December and faces a maximum of 20 years in prison. Jackson pleaded guilty to the same racketeering charge as Yee and is also scheduled to be sentenced in December.

Chow's trial is expected to last two weeks.