The FBI used millions of dollars, liquor and cigarettes seized in other cases and a dozen undercover operatives in a seven-year sting targeting a San Francisco Chinatown association thought to be a front for a notorious organised crime syndicate.
The agents, posing as businessmen and a mafia figure, aggressively offered their targets criminal schemes, leading to the indictment of 29 people - including state senator Leland Yee - on charges that included money laundering, public corruption and gun trafficking.
The agents' behaviour has become a central issue in the case, with defence lawyers arguing that the FBI entrapped otherwise honest people.
It's an argument numerous suspected terrorists, politicians and others have made when caught in a government sting.
In January last year, jurors in the state of Oregon rejected Mohamed Mohamud's claims that the FBI was at fault for him trying to set off a bomb during a 2010 Christmas tree lighting ceremony attended by thousands of people. The bomb, supplied by the agents, was a fake.
Undercover government agents are given wide room in setting up their targets, and Supreme Court rulings and Department of Justice guidelines make it clear they view sting operations as necessary and desirable to fight serious crime.
Entrapment claims work in court only in "extreme cases of outrageous government conduct", said Notre Dame University law school professor Jimmy Gurule, a former federal prosecutor and high-ranking US Department of Justice official under president George H.W. Bush.
In the San Francisco case, Gurule said federal prosecutors had to prove only that Yee and other targets of government stings were "predisposed to commit the crime".
Yee is accused of accepting thousands of dollars in campaign contributions in exchange for political help sought by FBI agents posing as business owners in need of influence in the state capital.
Defence lawyer Tony Serra is representing Raymond 'Shrimp Boy" Chow, the Hong Kong-born head of a Chinatown tong, or association, which the FBI says became a front for organised crime.
Serra said much of the government's case against Chow, Yee and the others was being driven by FBI operatives who were loaded with millions of dollars, were "wining and dining" their targets with US$250 shots of liquor at high-end restaurants and making persistent offers to break the law.
Serra said the US$58,000 Chow received from undercover agents were legal gratuities, not kickbacks for illegal activity.
"The undercover agents sought to induce him, sought to involve him, sought to catch him in some overt act that represented criminal activity," Serra said.
FBI spokesman Peter Lee declined to comment.