Former D.C. council member Michael A. Brown pleaded guilty in federal court on Monday to a bribery scheme that included cash stuffed in a Redskins mug and in a duffel bag with a Nationals baseball hat. (U.S. Attorney's Office for the District of Columbia )

He accepted $100 bills stuffed into a duffel bag alongside a Washington Nationals baseball cap. Another wad of cash came inside a Redskins coffee mug.

And detailed in Michael A. Brown’s guilty plea on bribery charges Monday was another revelation: evidence that the former D.C. Council member is cooperating with a broader investigation into a D.C. businessman connected to the secret financing of Mayor Vincent C. Gray’s 2010 campaign.

Brown, 48, admitted in federal court that he took $55,000 in cash from a company that he thought was trying to do business with the city government. In fact, the businessmen were undercover investigators with the FBI.

“Like many people after the economy crashed, Michael had extreme financial pressures, and they caused him to make a very unwise decision,” his attorney, Brian M. Heberlig, told reporters after Brown’s appearance at the U.S. District Court in Washington.

The prospect that Brown is cooperating in the larger investigation suggests that more charges against others are possible.

Brown’s connection to that investigation stems from a $20,000 contribution he received in his failed 2007 run for the D.C. Council. In his plea deal Monday, Brown acknowledged concealing the source of that contribution. The donor funneled the funds through public relations consultant Jeanne Clarke Harris, who in turn wired the money to Brown, who reported it as a personal contribution.

Harris pleaded guilty in July to orchestrating a scheme of illegal “straw” donations and an unreported “shadow campaign” of more than $600,000 benefiting Gray’s 2010 mayoral run, all financed by a co-conspirator unnamed in court documents.

Several people familiar with the investigation have identified the source of funds, including the donation to Brown, as businessman and major city contractor Jeffrey E. Thompson.

Ronald C. Machen Jr., the District’s U.S. attorney, said Brown will not be charged in connection with the campaign contribution. Prosecutors said Brown is cooperating, and they asked to push back his sentencing until October in light of that cooperation.

A 31-page court filing, meanwhile, described in detail Brown’s bribery scheme. He kept in constant touch with undercover agents who posed as businessmen seeking help becoming a “certified business enterprise” — a status that gives small, local or woman- or minority-owned contractors an advantage with city contracts.

According to court documents, the bribery scheme dates to conversations that began with an unnamed “Person A” prior to July. Brown asked the person to assist him in obtaining up to $75,000 from a government contractor in exchange for Brown’s help. That person arranged for Brown, then chairman of the D.C. Council’s Committee on Economic Development and Housing, to meet with one of the undercover agents.

In text messages, phone calls and five in-person meetings at D.C. restaurants including the Channel Inn and the Hamilton, Brown kept one of the undercover agents informed of his progress with the city’s bureaucracy. Brown also pressed the agent for partial payments, which he referred to as a “piece of the piece.”

On July 11, Brown received $15,000 in $100 bills stuffed in a duffel bag with two Washington Nationals T-shirts and a baseball cap. At another meeting, at the Channel Inn restaurant in August, an undercover agent handed over $10,000 in $100 bills placed inside a Redskins coffee mug. Brown left the restaurant with the mug and the cash, according to the court filing.

Machen noted after the plea hearing that Brown embarked on his illegal scheme after two of his D.C. Council colleagues had pleaded guilty to serious federal crimes. Harry Thomas Jr. (D-Ward 5) admitted in January 2012 to stealing $353,000 from city-funded youth programs, and former chairman Kwame R. Brown (D) pleaded guilty last June to a felony bank fraud charge.

“After seeing two of his former colleagues resign in disgrace, after promising voters that he had never violated the public trust, after hearing warnings from myself and from law enforcement, Michael Brown made the audacious choice to sell the public trust for cold hard cash,” Machen said. “The Maryland businessmen were not real, but what was real was Michael Brown’s willingness to put a for-sale sign on his D.C. Council seat.”

Brown occasionally referred to the payments from the sham company as a “loan,” according to prosecutors. But Machen said Brown “knew full well he was not expected to repay that money.”

“There was no discussion of an interest payment, there was no discussion of a repayment schedule. There were no loan documents that he signed. There was only cash, passed in secret,” he said.

During an eight-month-period, Brown made numerous calls to the Department of Small and Local Business Development, including to the director.

In one recorded phone call last August, Brown bragged about his access to government officials, saying that he may not know the specific employee at the department, but “Keep in mind, I know, whoever his boss is, that’s who I know.”

Harold B. Pettigrew Jr., the department’s director at the time, said Friday that Brown was among several council members who have contacted him seeking help for companies.

The final in-person meeting took place in March at a conference room at the Marriott Wardman Park hotel. Brown accepted $15,000 and an additional $5,000 bonus and the undercover agent discussed “doing more things together” if Brown were reelected the next month.

Law enforcement agents entered the room soon after and seized the cash from Brown.

Brown, who was elected to an at-large seat on the council in 2008 but lost a reelection bid last year, was seeking a political comeback at the time. Two weeks later, he dropped a bid to return to the council via an April special election. Machen confirmed Brown’s withdrawal was connected to the sting operation. If Brown had not withdrawn, he said, federal prosecutors were prepared to indict and arrest him.

Under federal sentencing guidelines, Brown faces jail time ranging from 37 to 46 months. As part of his plea agreement, he agreed to serve up to three years and one month and pay $35,000 — the money he collected before the final meeting with the undercover agents.