The D.C. businessman at the center of a long-running federal corruption investigation secretly spent more than $100,000 to help elect a D.C. Council member in 2008, according to a court filing and people familiar with the case.

Jeffrey E. Thompson, a former city contractor, had previously been implicated by prosecutors in funding unreported “shadow campaigns” on behalf of Mayor Vincent C. Gray (D) in 2010 and Democratic presidential candidate Hillary Rodham Clinton in 2008.

Another secret effort, on behalf of former council member Michael A. Brown, was laid out by prosecutors and attorneys for Brown in a joint court filing Friday.

Those papers describe Brown working with “Co-Conspirator 1” to have that person — Thompson, according to people familiar with the case — pay vendors’ bills that Brown’s campaign otherwise could not afford. The funds helped get-out-the-vote efforts for Brown in the final weeks of the council race in October and November 2008.

The new disclosure signals that prosecutors continue to build their case against Thompson, who has been implicated in six federal cases, including Brown’s. Charging papers and plea agreements have sketched out a campaign funding network that may have illicitly injected Thompson’s funds into dozens of national and local campaigns over a decade.

While many candidates benefitted from Thompson’s largess, only Brown has admitted knowing about illegal payments made to his campaigns.

The court papers, filed as part of a status report to the judge, describe personal meetings between Brown and Thompson at which the businessman made clear that his support must be kept hidden. The explicit nature of the arrangement between candidate and financier raises the question of whether Thompson may have made similar arrangements with other candidates.

Gray, for instance, has said he talked with Thompson about potential campaign support but has denied any wrongdoing. Prosecutors have recently investigated whether Gray may have repaid Thompson’s support by moving to settle a contract dispute between the city and his health-care firm — a suggestion Gray has strenuously rejected.

The payments made on Brown’s behalf were orchestrated by public relations consultant Jeanne Clarke Harris, who has admitted in court to helping Thompson organize the “shadow campaign” for Gray.

Thompson, the court filing said, did not want to be identified on the Brown campaign’s public finance reports “based on the contemporaneous political dynamics.” Brown, running as an independent, won the race and served one term as an at-large council member. He lost a reelection campaign and left office in January 2013.

Brian M. Heberlig, an attorney for Brown, declined to comment. William Miller, a spokesman for the U.S. attorney’s office in the District, would say only that the investigation continues. Brendan V. Sullivan Jr., an attorney for Thompson, did not return a message seeking comment but has steadfastly declined to address the nearly three-year-old investigation.

Brown pleaded guilty in June to a felony bribery charge, admitting to accepting $55,000 in cash from people he thought were businessmen seeking deals with the city government. In fact, they were undercover FBI agents who arrested Brown in a March 2013 sting after months of undercover operations.

Brown will not face additional charges as a result of the new disclosures, the papers indicate. But he could receive a longer sentence — up to 43 months in prison, rather than the 37-month maximum contemplated in the original plea agreement.

He had been scheduled to be sentenced April 28, but that date could be reset by U.S. District Chief Judge Richard W. Roberts.

As a part of his plea agreement, Brown agreed to cooperate with prosecutors as they conducted their wide-ranging city corruption investigation. The original charging papers filed in conjunction with the bribery plea also laid out a separate scheme for which Brown was not charged.

Brown admitted to accepting an illegal $20,000 contribution during his failed 2007 run for a D.C. Council seat. The money came from the same “Co-Conspirator 1” — again, Thompson, according to people familiar with the case — who funneled the money to Brown through Harris. Brown ended up reporting Thompson’s money as a contribution from his personal funds to his 2007 campaign.