SAN FRANCISCO >> Beneath the strings of red paper lanterns and narrow alleyways of the nation’s oldest Chinatown lies a sinister underworld, according to an FBI criminal complaint that has stunned even those familiar with the neighborhood’s history of gambling houses, opium dens and occasional gangland-style murders.

The federal charges, which allege a California lawmaker accepted money and campaign donations in exchange for providing official favors and helping broker an arms deal, cast harsh light on Chinatown’s tight-knit network of fraternal organizations and one of its most shadowy characters, Raymond "Shrimp Boy" Chow.

Investigators say Chow is the leader — the dragonhead — of one of the most powerful Asian gangs in North America. Chow’s gang is said to have lured state Sen. Leland Yee into its clutches through money and campaign contributions in exchange for legislative help, as Yee sought to build his campaign coffers to run for California secretary of state.

Born in Hong Kong in 1960, Chow came to the United States at 16 and was reportedly nicknamed "Shrimp Boy" by his grandmother, in part due to his small stature.

After dropping out of high school, Chow rose within the ranks of the local Hop Sing Tong gang after he and his crew survived a 1977 shooting at a Chinatown restaurant that left five dead and about a dozen people injured.

Chow then spent a few years inside San Quentin Prison for a robbery conviction, and after his release, he started working with the Hong Kong-based Wo Hop To triad, one of numerous Chinese underground societies linked to organized crime. Chow has admitted that as a gang leader, he ran prostitution rings, smuggled drugs and extorted thousands of dollars from business owners in the 1980s.

"He was given like an unofficial position of being a leader, but to say he was sophisticated, no. He was more like a forceful brute," said Ignatius Chinn, a former California Department of Justice agent who spent years investigating Chow in the early 1990s. "If he didn’t get his way, he would just beat the door down and that was how we put cases on him."

Although he ultimately was convicted of gun charges and sentenced to 25 years to life in the 1990s, Chow cut a deal to win release and returned Chinatown several years ago, pledging to stay straight. His work with at-risk youth soon won accolades from prominent politicians. But the complaint alleges that Chow used his position as the dragonhead of the Ghee Kung Tong to launder money, receive and transport stolen property and traffic in contraband cigarettes during a FBI sting.

Longtime residents and observers said the startling allegations revealed the continued presence of organized crime in the popular tourist attraction and home to one of the largest Chinese communities outside Asia.

"Chinatown is a very safe place and usually the crime you hear about there is just robberies and people being taken advantage of," said Joseph Leung, editor for the San Francisco edition of The Sing Tao Daily, the largest circulation Chinese newspaper in the U.S. "That’s why this is all so shocking."

The pre-dawn FBI raid Wednesday at the Ghee Kung Tong’s office, next to a massage parlor and across from a benevolent society where elderly people play Mah Jong, also brought into focus its centuries-old history. The tong was founded in the late 1880s to support immigrants from Hong Kong and elsewhere in the Pearl Delta region.

Amid morning rain showers Wednesday, federal agents and fire crews stormed the building armed with a circular saw and jaws of life to crack a safe that authorities say was at least a century old.

The organization is among dozens of active tongs, or family associations, in Chinatown, and Chow assumed control when its former president, Allen Leung, was shot to death by a masked gunman at his import-export store in 2006, said David Lee, director of the Chinese American Voters Education Committee.

"The killer was never caught and there was speculation that Shrimp Boy may have had something to do with it," said Lee, who also teaches political science at San Francisco State University. "He kind of became like a gangster celebrity. He was on parole, he had an ankle bracelet and he became a fixture at political events for a while."

The 137-page complaint, whose many twists are reminiscent of "American Hustle," does not reveal whether Yee had any connection to Chow before the FBI got involved.

Yee, a progressive Democrat born in China, built his political fortune partly through Chinatown connections and had never lost a race until his failed bid for San Francisco mayor in 2011.

A few years before that, Chow’s own political star began rising. Around 2008, he began meeting with at-risk youth to talk with kids about how to stay on the straight and narrow, said Rudy Corpuz Jr., executive director of the youth-led violence prevention organization United Playaz.

"He wasn’t just the average guy on the street corner when he had that life, he was somebody you wouldn’t mess with. And he’s little so people were like, ‘Damn, that little guy had that much power?" said Corpuz Jr., who said Chow’s redemption story helped change hundreds of young lives for the good.

Soon, the awards started coming. Chow was lauded by U.S. Sen. Dianne Feinstein of California for his work as a former offender who had become a community role model, and praised by San Francisco Mayor Ed Lee for his "willingness to give back to the community." He posted pictures of himself on Facebook with Lt. Gov. Gavin Newsom.

All the while he was running a criminal operation, according to court documents.

Several years ago, undercover FBI agents assigned to Chow infiltrated the organization, and ultimately snared Yee and his campaign consultant Keith Jackson.

The three were arrested Wednesday during a series of raids in Sacramento and the San Francisco Bay Area that also netted additional members of the tong.

Yee, free on $500,000 bail, withdrew Thursday from the race for secretary of state. Chow was denied bail because he was deemed a flight risk and a danger to the public. Jackson was denied bail, too.

"This is a very active criminal enterprise, and we won’t see this one very busy for the near future," Chinn said.

Yee’s allies, however, questioned why the senator had been targeted in the elaborate sting and cautioned that he was innocent until proven guilty.

"Leland always told me to be careful about taking money from the family associations, because you never know where the money is coming from. This kind of flies in the face of what he has told me," said Wayne Lee, a Yee protege recently elected mayor of nearby suburb of Millbrae. "He’s always been a champion for the downtrodden. I am hoping that he will be vindicated."