By David Ljunggren
OTTAWA (Reuters) - Canadian Senator Mike Duffy was acquitted of fraud and bribery charges on Thursday, marking the end of a high-profile trial that contributed to the defeat of the ruling Conservative government last year.
Duffy had faced 31 criminal charges related to roughly C$90,000 ($71,000) in expenses he charged after former Conservative Prime Minister Stephen Harper appointed him to the Senate - the upper chamber of Parliament - in late 2008.
The trial started amid enormous media coverage last August, shortly after Harper, who took power in 2006, had launched an election campaign.
As the case progressed, polls showed the Conservatives starting to lose support. The Liberals of Justin Trudeau, who said the affair showed Harper could not be trusted, won a majority in the federal election on Oct. 19.
Harper's chief of staff, Nigel Wright, told the court he had pressed Duffy to repay the expenses, even though he felt they were most likely legal.
Evidence showed that Harper's aides effectively took control of the leadership of the Senate, which is supposed to be independent, and provided Conservative senators with scripted lines. Emails indicated Wright had told one senator to approach an accounting firm that was carrying out an independent audit of the Senate, to try to influence its report.
In a 308-page ruling, Judge Charles Vaillancourt said he found Duffy to be a credible witness but blasted Harper's aides for their "mind boggling and shocking" conduct.
"In the context of a democratic society, the plotting ... can only be described as unacceptable," he told the court.
Duffy, a former television journalist, had been a popular fund-raiser for the Conservative Party before the scandal broke. He insisted all along he was innocent, saying the Senate's expense rules were so vague he had done nothing wrong.
"I don't think I've ever been witness to such a resounding acquittal," Duffy's chief lawyer Donald Bayne told reporters.
Duffy, who did not comment, was not the only senator to run into expenses problems. In June 2015, an official report found that 30 current and former senators had improperly spent almost C$1 million ($810,000) in just two years.
Trudeau is promising major reforms to the 105-member Senate, which is officially charged with reviewing legislation passed by the lower house. Senators are named by the prime minister of the day and the institution has historically been criticized as a dumping ground for political operators.
(Reporting by David Ljunggren; Editing by Paul Simao and Tom Brown)