Vernon Hawkins is accused of lying about trying to impede an investigation into an alleged “shadow campaign,” funded by businessman Jeffrey Thompson, to back Vincent Gray’s mayoral effort. (Marvin Joseph/The Washington Post)

New connections between Mayor Vincent C. Gray’s 2010 campaign and a prominent businessman’s alleged secret funding were revealed in federal court Tuesday, as an architect of the unreported $653,000 effort to elect Gray admitted to lying to investigators probing the case.

Vernon E. Hawkins, a longtime confidant of the mayor’s who held an informal advisory role in his 2010 campaign, told the court that he drew up plans and budgets for what became a “shadow campaign” allegedly funded by former city contractor Jeffrey E. Thompson.

Hawkins, 74, also described to prosecutors apparent coordination between Gray’s official campaign and the illicit operation, and detailed how he participated in a scheme to obstruct the federal investigation.

Prosecutors have not alleged that Gray (D) knew of the illicit happenings laid out in the Hawkins case or in previous prosecutions of campaign figures. But the admission of illegal activity by a man who was once among Gray’s most trusted political hands threatens to greatly complicate the mayor’s pending decision on whether to seek a second term. Gray has denied any wrongdoing.

Hawkins pleaded guilty to a count of making false statements — a felony charge for which, under his plea deal with prosecutors, he can expect to serve up to 16 months in prison.

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U.S. Attorney Ronald C. Machen Jr. said that Hawkins was “at ground zero of a scheme to design, staff, and execute an off-the-books shadow campaign.”

“This guilty plea takes us one step closer to understanding the extent of the deception that tainted the 2010 campaign,” he said in a statement released after the hearing.

In court papers and under questioning in the courtroom Tuesday, Hawkins described how he developed an independent “get-out-the-vote” effort for Gray starting in June 2010 through discussions with Jeanne Clarke Harris, a public relations consultant and close Thompson associate, and later with Thompson himself.

The operation was refined over the following weeks, Hawkins indicated, including in a conference call involving himself, Harris and Thompson. The secret effort included renting vans and hiring drivers, canvassers and coordinators to get Gray voters to the polls, the court papers said.

Thompson has not been identified in court filings, but several people familiar with the investigation say he is the “Executive A” referred to in several prosecutions, and court records show he is the subject of a grand jury probe. His attorney, Brendan V. Sullivan Jr., has declined to comment on the investigation and did not return messages seeking comment Tuesday.

Harris pleaded guilty last year to funneling Thompson’s money through companies she owned to fund the illegal effort for Gray, revealing for the first time the extent of the shadow campaign. Her attorney, Mark H. Tuohey III, declined to comment.

Detailed for the first time in the court papers filed Tuesday was an apparent relationship between the shadow campaign and Gray’s official campaign. The secret effort’s get-out-the-vote coordinator, identified in documents as “Person Two,” is said to have had an office on the same floor as Gray’s get-out-the-vote coordinator in a building adjacent to Gray’s campaign headquarters.

Several people familiar with the investigation identified “Person Two” as Tracy Hardy, a Philadelphia-based political consultant who told The Washington Post last year that he had coordinated with Hawkins but never worked for the Gray campaign.

According to the court documents, Hawkins told prosecutors he had “personally observed conversations between [Hardy] and [Gray campaign] officials during that time period.” The Gray campaign officials are not identified.

Hardy referred questions Tuesday to lawyer Joseph R. Conte, who said Hardy testified before a grand jury “a long time ago” and declined further comment.

The basis for the charge against Hawkins came well after the campaign, once federal investigators in 2011 began looking into allegations of improprieties. During that period, Hawkins said in court, he worked with Harris and Thompson to prevent at least one operative of the shadow campaign from speaking to investigators.

At times Tuesday, Hawkins — a silver-haired former high school football star who towered over the courtroom lectern — portrayed himself as a messenger for Harris and Thompson. He told U.S. District Judge Colleen Kollar-Kotelly that it was not his idea to have the campaign operative leave town.

“At no time was it my intent to have anyone not available for discussions,” he said, adding that it was “what Mrs. Harris and Jeff wanted” — a rare use of Thompson’s name in open court.

Hawkins acknowledged that on two occasions he gave envelopes from Harris — containing, he believed, a total of about $8,000 in cash — to “Person One,” making the handoffs in the parking lot of a Southeast Washington grocery store.

That person, according to people with knowledge of the investigation, is Lamont B. Mitchell, a resident of Southeast’s Hillcrest neighborhood and the owner of a catering business who allegedly handled transportation for the shadow effort. He did not respond to messages seeking comment Monday.

The cash, Hawkins said in court, was intended to support the operative while he stayed out of town during a period when investigators were seeking to interview him, in a bid to delay the probe. Two people familiar with the investigation said the money was Thompson’s.

In an August 2012 interview with federal authorities, Hawkins admitted that he untruthfully denied knowing any campaign figures who had been asked to leave town to avoid investigators or that he had personally asked or helped anyone to leave town.

At times under Kollar-Kotelly’s questioning, Hawkins seemed to downplay his false statements. “It happened so fast,” he said at one point. “I wasn’t thinking.”

But under questioning, Hawkins said he was aware he was misleading the investigators and potentially obstructing the probe.

“You know what you were saying was a lie?” Kollar-Kotelly asked Hawkins. “Is that correct?”

“Yes, your honor,” Hawkins said.

Gray has declined to discuss the charge against Hawkins, who served as a consultant and adviser in his successful D.C. Council campaigns dating to 2004.

The mayor held no public events Tuesday, and his attorney, Robert S. Bennett, declined to comment.

Hawkins and his attorney, William E. Lawler III, declined to comment as they left the courthouse Tuesday.

In a written statement, Hawkins apologized for “not being fully transparent” with federal authorities.

“This was a serious lapse, but it is an isolated one. I have dedicated my life to public service and to trying to improve the lives of all people who live in this city,” he wrote.

The charge against Hawkins carries a maximum sentence of five years in prison, but federal sentencing guidelines, as calculated as part of his plea deal, call for a more lenient sentence.

Nikita Stewart contributed to this report.