The man who worked as Mayor Vincent Gray’s campaign chauffeur pleaded guilty in D.C. Superior Court today to conspiracy to violate campaign finance laws.

Mark H. Long, who also served as Gray’s director of advance operations during the 2010 campaign, admitted to being paid for his services by Eugenia Harris with money from businessman Jeffrey Thompson, both of whom have pleaded guilty for their roles in a massive shadow campaign operated to benefit Gray. Gray has long denied any knowledge of these illegal activities, contradicting a claim by Thompson, who accepted a deal with the U.S. Attorney’s office in exchange for his cooperation.

Long “admitted knowing that Thompson and Harris intended to conceal, and did in fact, conceal, these payments from the Office of Campaign Finance,” according to the U.S. Attorney for the District of Columbia. He is also cooperating with the government as part of his plea.

“Mark Long’s guilty plea is further evidence that this 2010 mayoral campaign was rife with corruption,” U.S. Attorney for D.C. Ron Machen said in a release. “Long is now the sixth person associated with the 2010 mayoral campaign to become a felon as a result of illegal conduct on behalf of that campaign. Six months ago, when contractor Jeff Thompson walked into court and pulled back the curtain on widespread corruption in D.C. politics, we pledged to continue our work to hold accountable everyone who conspired with him to poison our political system. Since his plea, no fewer than four candidates for elected office in the District of Columbia have stood up in court and confessed to taking Thompson’s illegal contributions. Our work continues.”

According to Long’s statement of offense, the 47-year-old set up a meeting between “Mayoral Candidate A” — who has been publicly identified as Gray — and another mayoral candidate to encourage the rival — identified as Leo Alexander — to drop out of the race. According to prosecutors, Long also dropped off a package to a pro-Gray union official at Harris’ request. As the Post’s Mike DeBonis points out, Thompson claimed in his plea that he was directed by Gray to give $10,000 to a candidate “in a local labor run-off” election.