The NDP is calling on the federal prosecutions czar to review evidence collected by the RCMP during its investigation into Senator Mike Duffy to determine whether the prime minister's former chief of staff Nigel Wright or other PMO staffers, Conservative senators or party officials should face charges under the Parliament of Canada Act.

In a letter sent Tuesday to Brian Saunders, the director of public prosecutions, NDP's ethics critic Charlie Angus goes out of his way to praise the RCMP for what he describes as a "thorough and highly professional investigation."

In the letter, Angus says the Mounties "meticulously unpacked and sewed together an incredibly complex series of actions and behaviours, providing Canadians an unprecedented look into a scandal within the Prime Minister's Office."

In fact, Angus contends, documents made public as a result of that investigation revealed staff in the Prime Minister's Office, as well as sitting senators and party officials, "were aware of, and/or participated in the scheme to make a secret payment to a sitting senator, whitewash a Senate report, interfere in an external audit, all in an attempt to exonerate Senator Mike Duffy, who now stands charged with bribery and defrauding the Canadian public."

'Surprised' DPP not involved

Given that evidence, Angus says in his letter, he was "surprised to see that no one in this case was charged under the Parliament of Canada Act, which deals specifically with the legality of payments to senators."

He says he was also surprised to learn, via a statement from Saunders' office, that he "had no involvement in the Nigel Wright investigation" despite the DPP being "the service of jurisdiction in dealing with breaches of the Parliament of Canada Act."

Angus writes that the "unprecedented political sensitivities" that surround an investigation into the prime minister's inner circle "require the intervention of the [Director of Public Prosecutions]."

"(It is) incumbent upon the DPP to examine the evidence the RCMP has brought forward … against the laws and statutes of Canada, and explain to the Canadian people if an offence has occurred" — and if it hasn't, why not?

At a press conference in Ottawa Wednesday morning, Angus told reporters the RCMP investigation provided Canadians with "a picture of a potential conspiracy."

"When I read the Parliament of Canada Act, it says that it is illegal to offer money to a sitting senator for a matter that is of controversy," he noted.

"Mike Duffy was in the centre of a controversy, and all the people around him that were working on this deal — to me, it looks like it was under the Parliament of Canada Act, and I don't know why the RCMP decided not to look at the Parliament of Canada Act."

This, Angus said, is what he wants the director of public prosecutions to explain.

"I think [he] has an obligation to respond to us on this."

'Not an investigative agency'

A spokeswoman for Saunders's office confirmed receipt of the letter and said the office would respond to Angus "in due course," but did not offer much encouragement.

"The Public Prosecution Service of Canada does not discuss whether it is consulted or not regarding any case or investigation, as any consultation would be subject to solicitor-client privilege," Sujata Raisinghani told CBC News.

"The PPSC is not an investigative agency, nor does it lay charges in the matters it prosecutes ... those are the responsibility of law enforcement."

But Angus argues in his letter the DPP has a mandate to decide on prosecuting matters of the public interest and to communicate those decisions to the public.

Canadians need to be reassured, not "left with the impression that it is okay for the office of the prime minister to operate in an undefined ethical grey zone," Angus concludes.

"If there are no sanctions or consequences for such behaviour, it will leave Canadians thinking that Ottawa is indeed a very broken place in 2014."

Meanwhile, PMO spokesman Stephen Lecce was quick to point out the office assisted the RCMP in their investigation, "which," he said, "led to a number of criminal charges being filed against Mike Duffy."

"We have said all along: those who break the rules must suffer the consequences," he added.