RCMP Commissioner Bob Paulson has been asked to explain why the Mounties declined to lay charges against Nigel Wright, Prime Minister Stephen Harper's former chief of staff, over Wright's payment to suspended Senator Mike Duffy.

NDP ethics critic Charlie Angus has questioned Paulson about whether investigators discussed that decision with the director of public prosecutions or with anyone from Attorney General Peter MacKay's office.

Wright gave Duffy more than $90,000 of his own money to repay Duffy's questionable Senate living expenses.

Last week, the RCMP announced they didn't have evidence that Wright did anything wrong.

Angus says the allegations raised by the RCMP in court documents, which were heavily reported in the media, have raised "many disturbing questions."

"The fact the RCMP has decided not to follow through on the allegations with charges will certainly raise even more concerns, hence my decision to write to you," Angus said in the letter to Paulson.

The affidavit filed in court by RCMP investigators alleged a number of officials in the prime minister's office and in the Conservative Party were aware of negotiations with Duffy to cover expenses that they wanted him to repay.

"The fact that Conservatives acted to keep this deal secret, through the false claim that the money was obtained through a mortgage, certainly raised concerns over breaches of Parliamentary and Conflict of Interest statutes," Angus wrote in the letter.

Wright says he gave Duffy the money because he wanted taxpayers to be reimbursed. The RCMP affidavit suggests Duffy refused to use his own money to do so.

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