Hartford — A former U.S. attorney announced Thursday that his internal investigation of House Speaker Christopher Donovan’s congressional campaign turned up no evidence that Donovan was aware of or was involved in an alleged scheme to conceal the source of campaign donations.

Stanley Twardy Jr., now a partner at the Day Pitney law firm, released summary findings of his monthlong investigation during a morning news conference. Following the arrest in late May of the campaign’s finance director, Donovan’s campaign hired Twardy and his law firm to conduct the independent investigation and present the findings.

Twardy served as U.S. attorney for Connecticut from 1985 to 1991 and later as chief of staff for former Gov. Lowell P. Weicker Jr.

The Twardy investigation is separate from the ongoing FBI probe into contributions to Donovan’s campaign for the 5th Congressional District seat.

That federal probe led to the arrest of Robert Braddock Jr., Donovan’s then-campaign finance director, on charges that he conspired with others to hide the source of $20,000 in contributions. Donovan himself has not been charged with wrongdoing and denies any knowledge of what Braddock, a newcomer to Connecticut politics, is charged with doing.

Federal authorities contend that Braddock used straw donors to conceal contributions from someone he believed was an investor in “roll-your-own” smoke shops. That supposed investor — possibly an FBI agent — sought to stop a bill that would have imposed taxes on the smoke shops and their low-cost cigarettes. As speaker of the House, Donovan has significant influence over the fate of such legislation.

The smoke shop bill made it through the committee process but didn’t come to a vote during the General Assembly’s regular three-month session this spring, which ended before Braddock’s May 30 arrest.

However, the bill eventually became law after passing both the House and Senate during the legislature’s June special session. Donovan relinquished his speakership duties that day to avoid the perception of a conflict.

Twardy’s report describes how Donovan last fall met for breakfast with two individuals whom he understood to own roll-your-own smoke shops. The breakfast was arranged by Ray Soucy, a former union official for correction officers who has been identified in media reports as one of the unnamed co-conspirators in the alleged scheme.

The report says that smoke shop owners subsequently donated to Donovan’s campaign. Yet it was unclear whether Donovan exerted power to block the smoke shop tax bill, although the investigation found no record that he did.

On Thursday, Twardy said the goal of his investigation was to determine whether Donovan was involved in either concealing the true source of any campaign contributions or took part in any “quid pro quo” deals.

He said his probe didn’t find evidence of any such wrongdoing.

Twardy said he and nine members of his law firm were given “unfettered access” by the campaign. They interviewed Donovan in addition to a dozen of his current and former campaign staffers and legislative aides.

They also reviewed 165,000 pages of emails and 41,000 computer files and text messages from Donovan’s associates and the speaker’s own iPhone and iPad. The firm brought in Blum Shapiro to conduct a forensic audit and computer analysis of the campaign’s financial records. The team also checked deleted emails.

But Twardy acknowledged that his investigation was not definitive; he did not have subpoena powers, and four key members of Donovan’s campaign staff refused interviews.

Three of the four had been fired by the campaign: Braddock, Joshua Nassi, the former campaign director, and Sara Waterfall, former deputy finance director. The fourth, Laura Jordan, one of Donovan’s campaign aides, declined through her lawyer to allow an interview.

Donovan is the endorsed Democrat in the race for the seat of U.S. Rep. Chris Murphy, a fellow Democrat who is running for U.S. Senate. He enjoys strong union support.

One of Donovan’s Republican opponents declared that the Twardy investigation is far from conclusive as “people who commit crimes are not often reckless enough to leave a paper or email trail. The absence of such documentation is not surprising.”

The opponent, Mark Greenberg, continued: “The cloud of this campaign finance scandal will continue to hang over Donovan’s campaign until the federal investigation is concluded.”

Donovan’s new campaign manager, Tom Swan, said the House Speaker is “very much looking forward to getting back to what this campaign is about — Chris’s long record of fighting for Connecticut’s families.”

j.reindl@theday.com