SAN FRANCISCO (AP) — The FBI used millions of dollars, liquor and cigarettes seized in other cases and more than a dozen undercover operatives in an elaborate, seven-year sting operation targeting a San Francisco Chinatown association thought to be a front for a notorious organized crime syndicate.

The agents, posing as honest businessmen and a Mafia figure, spent freely and aggressively offered their targets criminal schemes, leading to the indictment of 29 people — including state Sen. Leland Yee — on charges that included money laundering, public corruption and gun trafficking.

The agents' behavior has already become a central issue in the month-old case, with defense lawyers arguing that the FBI entrapped otherwise honest people by luring them into criminal schemes hatched by the government.

It's an argument numerous suspected terrorists, politicians and others have made when caught in a government sting.

But legal experts say the entrapment defense rarely works. Sting targets have to prove much more than simply the government made them do it. They have to show they weren't predisposed to committing the criminal acts proposed by undercover agents.

Several high-profile terrorism suspects in recent months have argued they were set up by undercover agents who played central roles in helping them plan U.S. attacks that they otherwise would never have intended to carry out.

In January 2013, jurors in Portland, Ore., rejected Mohamed Mohamud's claims that the FBI was at fault for him trying to set off a bomb at Pioneer Courthouse Square during a 2010 Christmas tree lighting ceremony attended by thousands of people. The bomb, supplied by the agents, was a fake.

In December, a federal appeals court rejected Mohanad Shareef Hammadi's claims that he was entrapped when he unwittingly worked with an government informant to ship thousands of dollars in cash, machine guns, rifles, grenades and shoulder-fired missiles from Kentucky to al-Qaida in Iraq from 2010 through 2011. No money or weapons ever left the United States.

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"Entrapment is often raised but seldom successful," said Notre Dame University law school professor Jimmy Gurule, a former federal prosecutor and high-ranking U.S. Department of Justice official under President George H.W. Bush.

Undercover government agents are given wide latitude in setting up their targets, and U.S. 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," Gurule said.

In the San Francisco case, Gurule said federal prosecutors have to prove only that Yee and other targets of government stings were "predisposed to commit the crime."

When the FBI targets politicians, Gurule said the investigators usually need valid reasons to approach them with bribe offers, such as evidence or reports of previous solicitations. Agents, he said, look for a pattern of behavior.

"The FBI is not going to approach every politician with a bag full of money," Gurule said.

Yee was arrested March 26, the same day FBI agents arrested Charlotte, N.C., Mayor Patrick Cannon, who is also accused of taking bribes from undercover agents posing as business people seeking political favors or influence.

The mayor accepted cash from agents posing as real estate developers in exchange for access to city officials responsible for planning, zoning and permitting, the complaint said.

On the last occasion, a private meeting in the mayor's office on Feb. 21, the developer gave Cannon a briefcase containing $20,000. Cannon's attorney James Ferguson II said no decisions have been made regarding a defense.

"We are still gathering factual information and researching the law as we prepare Mr. Cannon's case," Ferguson said.

Senator Yee has pleaded not guilty and his attorney, Jim Lassart, declined to comment on his defense. Yee's previous attorney, Paul DeMeester, said last month that "entrapment is always a defense you can consider, but we have to look at all the evidence."

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 Sacramento.

J. Tony Serra, a long-time defense attorney, is representing Raymond 'Shrimp Boy" Chow, the head of a Chinatown tong, which the FBI says became a front for organized crime.

Serra said much of the government's case against Chow, Yee and the others is being driven by FBI operatives who were loaded with millions of dollars, were "wining and dining" their targets with $250 shots of liquor at high-end restaurants and were making persistent offers to break the law.

Serra said the $58,000 Chow received from undercover agents were legal gratuities, not kickbacks for illegal activity. Chow has pleaded not guilty.

"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.

Garrick Lew, who represents another defendant in the San Francisco case, complained in court that FBI agents significantly overpaid thousands of dollars each for guns worth a few hundred dollars apiece allegedly sold by his client, Rinn Rouen, who has pleaded not guilty to gun trafficking and murder for hire charges.

"The FBI was throwing money at people," said Lew.

FBI spokesman Peter Lee declined to comment.