A Conservative senator and his aide say they were told 18 months ago that Liberal MP Raj Grewal was under investigation for his prodigious casino gambling, and argue it is “unbelievable” that Prime Minister Justin Trudeau’s office didn’t know at the same time.

And if the PMO knew then, they say, it should not have taken until last week for Grewal to resign his Toronto-area seat — and until this September for him to be shifted off the Commons finance committee.

Quebec Sen. Jean-Guy Dagenais and assistant Richard Desmarais say they were at an Ottawa reception in May of 2017 when a retired RCMP officer told them he had been informed about a probe of Grewal.

“(He) told us, ‘Just check this guy at the casino. He is spending a lot, he’s under inquiry, and something will happen,’“ Desmarais said in an interview Thursday. “He said, ‘You can go, you will see him, spending his money, he is under an inquiry’ … If the prime minister’s office didn’t know that, it’s unbelievable.”

An RCMP spokeswoman said privacy rules bar it from even confirming whether or not the agency is investigating Grewal.

If the prime minister’s office didn’t know that, it’s unbelievable

Chantal Gagnon, a spokeswoman for Prime Minister Justin Trudeau, referred the Post to an earlier statement saying their office only learned of the gambling situation last week.

Desmairais said it was unclear during the conversation — which took place at an event for former police members — whether the investigation the retired officer mentioned was underway at the time was being conducted by the RCMP or by another agency.

But even the casino security department would have informed the Mounties if it were scrutinizing a sitting MP, and that would have raised red flags at the force, he suggested.

“It is impossible that the RCMP doesn’t know where he is sitting, on which committee he is acting and everything like that,” said Desmarais. “Knowing that, they have to tell the prime minister’s office.”

Dagenais, himself a former officer with the provincial Sûreté du Québec force, raised the issue in the Senate Wednesday, even as other aspects of the Grewal affair dominated the House of Commons question period Thursday.

The MP for Brampton East announced last week he was quitting the Commons, initially saying it was for “personal and medical” reasons. Prime Minister Justin Trudeau Tweeted in a similar vein, saying the backbencher was “facing serious personal challenges.”

But the next day, the PMO acknowledged it had learned earlier last week that Grewal had been having gambling problems and racked up considerable debt, while the RCMP was looking into a separate ethics issue. The MP himself later issued a statement acknowledging his gambling addiction.

It is impossible that the RCMP doesn’t know where he is sitting, on which committee he is acting and everything like that

Quoting unnamed sources, the Globe and Mail reported this week that the RCMP had been investigating Grewal for “several months” over financial transactions related to the millions of dollars he spent at casinos.

According to a source quoted by The Canadian Press, Grewal’s name and gambling debts surfaced on wiretaps that were part of a broader probe of organized crime and terrorist financing.

Now questions are being raised about Grewal’s role on the finance committee, especially after he questioned law-enforcement witnesses at hearings earlier this year about how they investigate money laundering.

The Liberals moved him off the committee Sept. 19, but say it was not related to any investigation of him.

In the Senate Wednesday, Dagenais asked if the PMO was investigating whether Grewal had access to confidential documents on money laundering or terrorist financing as a committee member.

Sen. Peter Harder, a government representative, said he would take the question under advisement, but Desmarais said Thursday the senator had yet to receive an answer.

• Email: tblackwell@nationalpost.com | Twitter: TomblackwellNP