Shirley Lasseter abruptly resigned as Gwinnett County commissioner Thursday before pleading guilty to taking $36,500 in bribes in an ongoing corruption investigation that ensnared her son and a businessman described as Lasseter's "bag man."

Lasseter pleaded guilty to one count of bribery. Her son, John Fanning, a member of Gwinnett's Zoning Board of Appeals, and Hall County businessman Carl "Skip" Cain also pleaded guilty to the bribery scheme and to federal drug charges. They will be sentenced Aug. 6.

If the pleas were not enough to shake up the county government, federal prosecutors disclosed that more prosecutions involving land deals could be forthcoming. At Thursday's hearing, Assistant U.S. Attorney Douglas Gilfillan said all three defendants are now talking to authorities and could receive reduced sentences based on the value of their cooperation in other investigations.

Lasseter becomes the third Gwinnett commissioner in less than two years to resign from office amid accusations of wrongdoing. Chairman Charles Bannister and Commissioner Kevin Kenerly resigned in 2010 in the wake of a grand jury investigation of dubious land deals. Kenerly was was eventually indicted on bribery charges.

Lasseter pleaded guilty Thursday to taking the bribes last year in exchange for her agreement to vote for a proposed real estate development in her district on Boggs Road. An undercover FBI agent posing as a businessman gave the payoffs to Lasseter in cash. He also told the commissioner he laundered illegal drug proceeds and was using that money to buy the Boggs Road property, Gilfillan said.

During one meeting, Lasseter and Fanning tried to enlist the undercover agent to become Lasseter’s “bag man” to secure more bribes, Gilfillan said. Lasseter considered herself a swing vote on the privatization of Briscoe Field, the county's airport, and could leverage that to rake in more payoffs, he said.

Cain, who lives in Flowery Branch and runs a trucking business, had previously been a "bag man" for both Lasseter and Fanning, Gilfillan said, citing a secretly recorded conversation involving Lasseter and Fanning with the undercover agent. He did not elaborate further on any previous incidents.

After hearing Gilfillan outline the facts of the case, U.S. District Judge Charles Pannell Jr. asked Lasseter why she did what she did.

"Your honor, I truthfully regret I took a bribe," said the 64-year-old Lasseter, who was represented by a federal public defender. "I am very ashamed I did something like that to embarrass not only myself and my constituents but also the commissioners in Gwinnett County."

Pannell then asked, "You did it for the money?"

"Yes sir," she answered.

When notifying County Administrator Glenn Stephens Thursday of her resignation, Lasseter wrote, "I deeply regret the harm I have caused to those I have served and the trust I have betrayed. Please know that I am ashamed of my actions. I am doing everything I can to right the wrongs in which I have engaged."

Lasseter, a Republican, was elected to the Board of Commissioners in 2008 and represented District 1. She previously served as mayor of Duluth for 14 years.

Gwinnett spokesman Joe Sorenson said county officials are still trying to determine whether and how they must fill Lasseter’s commission seat for the remainder of her term, which expires at the end of this year. Lasseter had already announced she was not seeking re-election.

At the plea hearing, Lasseter sat next to her son, whom she appointed to the Gwinnett zoning board in February 2011. Fanning, of Dacula, runs a landscaping business and envisioned laundering money at a pawn shop on the Boggs Road property, Gillfillan said.

Fanning was in the thick of the bribery scheme and was easily coaxed by the undercover agent into a phony money laundering and drug dealing operation, the prosecutor said.

Lasseter became a target in an ongoing investigation by the FBI and Gwinnett law enforcement into public corruption involving land deals.

After the plea hearing, Gwinnett District Attorney Danny Porter said he asked federal authorities for their help two years ago. “We have to be rid of this culture of corruption that exists in Gwinnett County,” he said.

According to court records, the undercover FBI agent, first met Lasseter at a Gwinnett hotel on June 15, 2011. Before the meeting, Cain told the undercover agent Lasseter was in financial distress and needed $1,500.

When Lasseter arrived, the agent took her aside and gave her $1,500 in cash. The undercover agent also told Lasseter he was happy to help her in the future because he would later need her vote.

"You've got my vote," Lasseter responded, the complaint said.

On July 1, Cain, described in the court documents as being an "associate" of Lasseter's, told the agent that Lasseter wanted $35,000 in exchange for her vote on the Boggs Road development.

Almost three weeks later, Lasseter, Fanning and Cain attended a social function with the agent in South Florida, during which the agent gave Lasseter $9,000 in cash as a partial payment for the $35,000 bribe, a federal complaint said.

When the undercover agent handed over the cash to Lasseter, he asked, "We're good?"

"We're great," Lasseter replied.

In August, Lasseter received the final $26,000 payoff from the undercover agent at an Atlanta hotel. During that meeting Lasseter and Fanning each counted the dollars, "roll by roll," Gilfillan said.

Before the undercover agent left, he told Lasseter and Fanning that he was laundering money for drug traffickers and said some of that money was being used to pay for the Boggs Road project, Gilfillan said.

The undercover agent had previously asked Fanning whether he was willing to become involved in illegal money laundering. According to the complaint, Fanning was all in.

"I'm totally on board," he said. "I don't mind doing any of this and I've definitely done things under the table before my whole life. I mean, I got no problems doing stuff like this. That's how we all get by," the complaint said.

In September, the complaint said, Fanning and Cain flew to the New York area to retrieve what they thought would be a multiple-kilogram shipment of cocaine. They spent the night and flew back with "four kilograms of purported cocaine," the complaint said.

Fanning and Cain each took possession of two kilograms of the substance so they could give it to a prospective buyer, but were apprehended before making the deliveries, Gilfillan said.

At the plea hearing, Pannell asked Cain, 65, why he got involved in such an operation.

"Money, sir," answered Cain, who also accepted a $10,000 bribe.

Fanning, 34, told the judge he'd made "a very stupid mistake."

"I'm still very young, still learning a lot," he said. "I made a bad mistake. I got in over my head, your honor."

U.S. Attorney Sally Yates said the guilty pleas are an part of "an ongoing effort to root out public corruption in Gwinnett County."

In October 2010, a special Gwinnett grand jury investigating suspicious county land deals indicted then-Commissioner Kevin Kenerly for bribery. Kenerly resigned soon afterward but maintained his innocence and challenged his indictment, which is still pending.

The grand jury also considered a perjury charge against then-Chairman Charles Bannister for his testimony during the investigation, but decided not to pursue the charge when Bannister resigned. The grand jury concluded Gwinnett paid millions of dollars too much for land in deals that benefited friends and political allies of several commissioners.