According to court documents, Democratic California State Senator Leland Yee's political career began to unravel "at some point in the last five years" when an undercover FBI agent was introduced to a self-described reformed gangster who operated in San Francisco's Chinatown named Raymond "Shrimp Boy" Chow.

In an affidavit filed in federal court on March 23, FBI special agent Emmanuel Pascua detailed how the investigation into Chow led to Yee's arrest on political corruption and gun-trafficking charges last Wednesday. It's an incredible saga that includes purported links to Chinese organized crime, a crooked political consultant, Eastern European arms dealers, and Muslim rebel groups in the Philippines.

Yee's arrest derailed his campaign for secretary of state. He withdrew from that race Thursday, and the following day the Legislature voted to suspend him from the State Senate. On Monday, though Yee's lawyer indicated that he will plead not guilty, Gov. Jerry Brown called for him to resign.

Yee's implosion reportedly shocked California politicos, especially since Yee was, in the words of The Los Angeles Times, "a hero of gun regulators" after pushing for legislation that would have strengthened the state's assault-weapons ban after the 2012 school shooting in Newtown, Conn. After that shooting, Yee issued a statement calling for tougher gun-control restrictions.

"We must limit access to weapons that can result in such catastrophe and mass murder," Yee said.

However, according to Pascua's complaint, while publicly promising to curb access to guns, Yee was holding private meetings with people he thought were mafia associates promising to connect them with people who could provide heavy weaponry.

Pascua said Yee attracted the attention of the FBI through Chow, who was described in the complaint as "the Dragonhead, or leader, of the San Francisco-based Chee Kung Tong organization." According to Pascua, the Chee Kung Tong "is believed to be an offshoot of the Hung Mun … also referred to as a Chinese secret society and the Chinese Freemasons, among other names," which "began in China sometime in the mid-17th century as a result of a revolutionary movement to overthrow the Manchu-ruled Qing Dynasty."

"The CKT and its criminal activities have been of interest to law enforcement since at least as early as 2006, when the CKT's previous Dragonhead, Allen Leung, was murdered in San Francisco," Pascua said.

The headquarters of the Chee Kung Tong was one of multiple locations raided by the FBI Wednesday morning (pictured at right) as Yee, Chow, and others were arrested.

Chow has a lengthy criminal record, including a conviction for robbery and a 2000 guilty plea for racketeering, which Pascua described as "involving murder-for-hire, conspiracy to distribute heroin, arson, and conspiracy to collect extensions of credit." According to Pascua, Chow was "sworn in as Dragonhead" after he was released from prison following that plea in 2006. By May 2010, Pascua said multiple FBI undercover agents had infiltrated the Chee Kung Tong and gotten to know Chow.

"Based on information that has been received by FBI agents from confidential human sources, as CKT Dragonhead Chow holds a '489' position in the Triad, which is an internationally based Chinese organized crime group. The '489' position signifies supreme authority within the Triad," said Pascua.

One of the undercover agents claimed to have mafia connections on the East Coast, Pascua said, and Chow eventually introduced them to Jackson. According to Pascua's affidavit, Jackson went on to develop an extensive "criminal relationship" with the undercover agent that included selling them weapons and "ballistic vests," planning various drug deals, and introducing them to people who provided stolen credit cards and expressed willingness to engage in murder-for-hire.

Pascua described Jackson as a "consultant" to Chee Kung Tong as well as a "close associate" and fundraiser for Yee. In May 2011, Pascua said, Jackson began asking the undercover agent to donate to Yee's mayoral campaign. However, Pascua claimed the undercover agent declined to give money to Yee and instead introduced Jackson to another undercover agent they described as a "business associate" who gave "at least one personal donation in the amount of $5,000."

Yee lost the mayoral election in November 2011. Afterward, he had $70,000 in campaign debt. As Yee prepared to run for secretary of state, Pascua said he and Jackson sought donations to retire that debt from the second undercover agent.

"Senator Yee and Keith Jackson agreed that Senator Yee would perform certain official acts in exchange for the donations." Pascua said.

Yee allegedly agreed to do deeds for three different undercover agents in exchange for campaign cash. They included making a phone call to an official encouraging them to give one of the agents a contract, writing "an official letter of support," providing a State Senate proclamation honoring the Chee Kung Tong, an introducing an undercover agent who posed as a "businessman involved in medical marijuana" to lawmakers who could influence pot legislation.

Pascua said Yee and Jackson collected over $30,000 for these various actions.

In August of last year, Pascua said Jackson told one of the undercover agents Yee had "a contact who deals in arms trafficking." According to the affidavit, Jackson said Yee could facilitate a meeting about weapons deals in exchange for more campaign contributions.

On Dec. 3, 2013, according to Pascua, Jackson met with the undercover agent who was posing as a mobster to discuss various "illegal business opportunities" including cocaine deals and hiring hitmen. At that meeting, Pascua said Jackson told the undercover agent he "spoke with Senator Yee about the opportunity to traffic firearms" and was confident Yee's connection was the "real deal."

In January, Pascua said Yee met with Jackson and the undercover agent at a coffee shop where he said the arms dealer "sourced the weapons from Russia" and described them as having contacts in "Russia, Ukraine, Boston, and Southern California."

"Do I think we can make some money? I think we can make some money," Yee said, according to Pascua's affidavit. "Do I think we can get the goods? I think we can get the goods."

In addition to assuring the undercover agent of his ability to get weapons, Pascua said Yee described visiting the Philippines and encountering "armed guards with machine guns."

"It's not just Russia. The Muslim countries have sources too," Yee allegedly said. "And so, that has been brought to my attention recently."

According to Pascua, the undercover agent told Yee and Jackson he wanted up to $2.5 million worth of firepower including "shoulder fired" weapons or missiles and promised to provide them with $100,000 for facilitating a meeting with the arms dealer.

In February, Pascua said Yee, Jackson, and the undercover agent met again and the state senator dismissed ethical concerns about the weapons deal, saying, "People want to get whatever they want to get. Do I care? No, I don't care. People need certain things." Yee also allegedly described being unhappy and expressed his desire to emulate the agent, who he thought was a mobster.

"There is a part of me that wants to be like you," Yee said, according to the affidavit.

On March 4, Pascua said Jackson called the agent to say Yee wanted to "shift to another source to get weapons," Dr. Wilson Lim, a dentist. According to the affidavit, Yee and Jackson allegedly introduced Lim to the agent at a restaurant eight days later. At that meeting, Pascua said Yee implied Lim was connected to a Muslim rebel group in the Philippines, the Moro Islamic Liberation Front.

Yee, Jackson, Lim, and Chow were all named in a federal indictment along with over 20 other people. Some of the charges against Yee carry possible sentences of up to 20 years in prison. Yee is free on a $500,000 bond.

On Monday, his lawyer Paul Demeester said Yee would plead not guilty and suggested the length of the investigation indicated law-enforcement agents were searching for "a case they could make" against Yee and entrapped him into the weapons deals.

"The agents started pushing this idea of the arms dealing," Demeester said.

Demeester did not immediately respond to a request for comment from Business Insider Monday evening. Yee is next due in court April 8.