By Louise Egan
OTTAWA, April 15 (Reuters) - Canadian police on Tuesay dropped an investigation into Prime Minister Stephen Harper's former chief of staff whom they suspected of corruption in connection with a Senate expenses scandal that hurt the Conservative government's popularity.
Police had suspected Nigel Wright, Harper's former chief of staff, might have acted corruptly in early 2013 when he wrote a personal check for C$90,000 ($82,000) to help disgraced Senator Mike Duffy repay housing expenses he had wrongfully claimed.
The Royal Canadian Mounted Police (RCMP) said in a statement that when they began their probe in June they had sufficient grounds to look into possible charges of breach of trust, bribery, fraud and violations of a parliamentary law on compensation.
"Upon completion of the investigation, we have concluded that the evidence gathered does not support criminal charges against Mr. Wright," RCMP spokeswoman Corporal Lucy Shorey said.
In a scandal that exploded in May, Senator Duffy and two other senators - Pamela Wallin and Patrick Brazeau - were found to have inappropriately claimed housing expenses. All three were subsequently suspended from the Senate and subject to police investigation.
Duffy, a former television journalist and successful fundraiser for the Conservatives, paid back what he owed. But Harper was later forced to acknowledge that Wright had provided Duffy with the cash for that payment.
Canadian law forbids people from offering legislators money that is linked to their official duties.
Harper initially defended his aide but later condemned his actions and Wright departed soon after. Harper insisted he did not know about the payment and wouldn't have allowed it if he had.
He also denied allegations by Duffy that the prime minister's office had schemed to cover up the payment.
The opposition parties attacked Harper's credibility and the Conservative party's popularity slipped in the polls. The next election is not until October 2015.
Harper's office issued a guarded statement on Tuesday.
"We are pleased the RCMP has made progress in their work," it said, pledging to cooperate with ongoing investigations.
Wright, a wealthy businessman seconded to Harper's office from his private equity firm, had always claimed his actions were legal.
"My intention was to secure the repayment of taxpayer funds. I believed that my actions were always in the public interest and lawful," he said in a statement through his lawyer.
"The outcome of the RCMP's detailed and thorough investigation has now upheld my position."
($1 = $1.10 Canadian dollar) (Editing by Jeffrey Hodgson and Cynthia Osterman)