A third person associated with businessman Jeffrey E. Thompson admitted to making illegal campaign donations on his behalf Monday, as the District’s top federal prosecutor said his wide-ranging probe of political corruption continues.

Stanley L. Straughter of Philadelphia pleaded guilty in U.S. District Court to a misdemeanor count of making unlawful corporate contributions, saying he made $132,600 in political donations under his name, his company’s name and the names of relatives, when in fact the money came from a D.C. accounting firm and its chief executive.

Several people familiar with the investigation have identified the executive as Thompson, founder of the firm Thompson, Cobb, Bazilio and Associates, and a longtime city contractor.

Thompson is also alleged to have secretly financed a $653,000 effort to help Mayor Vincent C. Gray (D) get elected in 2010. Gray has denied any wrongdoing.

Straughter, 71, is an international development and trade adviser who has been associated with several overseas for-profit and charitable undertakings. He was named an honorary consul for Guinea and chairs a commission on African and Caribbean immigrant affairs for Philadelphia Mayor Michael A. Nutter (D).

Although Straughter is listed in some biographical notes as being a director of Thompson, Cobb, Bazilio and Associates, court documents said he was a contractor providing “marketing and consulting services.” Starting in 2006, according to court papers, Straughter was reimbursed for political donations made at Thompson’s behest with funds from the accounting firm.

Steven J. McCool, Straughter’s attorney, did not acknowledge Thompson’s connection to the case and did not discuss Straughter’s reasons for participating in the “straw donor” scheme, except to say he is a “good and . . . decent man” who “exercised poor judgment.”

“He’s going to continue to cooperate with the government, and he’s going to fulfill his end of the bargain,” McCool said.

An employee of the accounting firm, now called Bazilio Cobb Associates, pleaded guilty to a similar charge last week. Lee A. Calhoun said he made $160,000 in donations using funds from Thompson and the firm.

Jeanne Clarke Harris, a public relations consultant with close ties to Thompson, admitted to helping to orchestrate a Thompson-funded straw donor network last July, in a guilty plea that also revealed the scope of the secret Gray “shadow campaign.”

Thompson has not been charged in connection with the shadow campaign or the “straw donation” schemes court documents allege he orchestrated. His attorney, Brendan V. Sullivan Jr., has declined to comment, citing a policy of not discussing pending cases.

Charging documents in the Straughter case identify contributions made in 2010 that appear to match donations listed in federal campaign records to Del. Eleanor Holmes Norton (D-D.C.) and the late senator Arlen Specter (D-Pa.).

District, Maryland and federal campaign finance records show Straughter and family members making at least $102,000 in political donations dating to 2006, when the illegal arrangement with Thompson is said to have begun. The recipients included D.C. Council members Yvette M. Alexander (D-Ward 7), Muriel Bowser (D-Ward 4) and Vincent B. Orange (D-At Large), as well as mayoral candidates Linda W. Cropp, Adrian M. Fenty and Gray.

The most frequent beneficiary of Straughter’s largess appears to be Hillary Rodham Clinton’s 2008 presidential campaign, which garnered a combined $13,800 from Straughter and his wife. Thompson held a 2007 fundraiser for Clinton in the Thompson, Cobb, Bazilio offices downtown.

Straughter faces a maximum sentence of one year in prison and a $100,000 fine. A sentencing date has not been set.

“We are encouraged that Mr. Straughter acknowledged responsibility for participating in this scheme and has agreed to cooperate with the government,” the District’s U.S. attorney, Ronald C. Machen Jr., said in a statement. “Our investigation into these matters continues.”