Republican Jim McKenna refused to back off his claim Tuesday that Attorney General Martha Coakley granted disgraced former Sen. Dianne Wilkerson "immunity" in her campaign finance violations case as Coakley aides and her predecessor disputed McKenna's description of the settlement.

Attacking Coakley's record on public corruption, McKenna, the Republican candidate for attorney general, repeated the charge first leveled in a televised debate over the weekend.

The Republican's comments, however, revived questions about his use of the term "immunity" and his characterization of a 2008 settlement the state reached with Wilkerson prior to her indictment on federal bribery charges.

"There is no doubt that Martha Coakley gave Dianne Wilkerson immunity," McKenna said during a morning press conference Tuesday with Republican gubernatorial candidate Charles Baker.

McKenna's campaign provided copies of what he described as the "smoking gun," circulating a settlement statement signed off on by Coakley's office dispensing with a lawsuit filed against the former senator for accepting illegal campaign contributions between 2000 and 2008.

Wilkerson admitted to and was fined for the violations, under the agreement. The settlement exempted Wilkerson from future prosecution for campaign finance violations prior to 2008 - a period during which the F.B.I. now claims she was accepting bribes.

A little more than a month after the agreement was signed, Wilkerson was indicted on federal bribery charges.

McKenna said the document proves that Coakley gave Wilkerson a "get out of jail free card." "She was accepting bribes at the time Martha Coakley gave her immunity," McKenna said, acknowledging that she has, in fact, been prosecuted for those crimes.

Coakley's campaign harshly dismissed the accusations, suggesting McKenna's willingness to continue with his line of attack raised questions about his ability to serve as attorney general.

"Jim McKenna's continued statements on this subject demonstrate either a blatant misunderstanding of the law or a disturbing willingness to mislead voters," said Corey Welford, spokesman for Coakley's campaign.

In a strict legal sense of the word, state statute prohibits immunity from being granted in cases involving campaign finance violations. Immunity also requires approval from a judge, neither of which happened in Wilkerson's case.

Wilkerson admitted to taking $2,200 in illegal campaign contributions, including $250 from an unregistered political action committee, $550 from for-profit businesses and $1,400 from individual contributors in excess of contribution limits.

She also admitted to operating her campaign committee without a treasurer, and agreed to release the committee from more than $23,500 she claimed she was owed from her campaign.

Wilkerson agreed to pay a $10,000 fine, and submit to increased oversight over her campaign finance filings.

The settlement statement, signed off on by Coakley's office in July 2008, released Wilkerson from "further liability based on campaign finance reports filed by the Committee prior to the date of this Agreement, and from all civil, criminal, or administrative claims and charges under G.L.c. 55 based on acts or omissions occurring on dates up to and including December 31, 2007."

Chapter 55 of the Massachusetts General Laws relates specifically to campaign finance law.

Welford said the clause did not preclude the state from pursuing other charges such as bribery prior to 2008, and did not prohibit the corruption charges brought by the federal government for which Wilkerson is now awaiting sentencing.

At the very least, McKenna's campaign said he would never have entered into a settlement agreement with Wilkerson knowing that she already had a history tax evasion.

"She should have been prosecuted to the full extent of the law," said McKenna spokeswoman Laura Rigas.

Former Attorney General Thomas Reilly, who brought the initial case against Wilkerson, said McKenna's argument shows "a rather shocking lack of knowledge of the law."

"It's ridiculous," Reilly said. "There's a very specific statute on immunity in this state."

Reilly said the clause in question was a "common part" of civil settlements, and not a "broad release" from future prosecution for other crimes.

"It was very difficult to deal with Senator Wilkerson. Let me put it that way. This agreement was a very good job by the attorney general's office to bring closure to this case. I would have signed off on the same agreement if it came to my desk," Reilly said.