The bombshell revelation of a police investigation into an alleged sexual assault by a Conservative candidate during the 2015 election triggered a heated debate that split Stephen Harper's inner circle, CTV News has learned.

The most powerful woman on the campaign, Jenni Byrne, argued that Rick Dykstra should be fired. However, a toxic environment among the senior staff compromised decision making, sources tell CTV’s Mercedes Stephenson.

Party insiders, including Ray Novak, say that if they knew then what they know now, Dykstra would have been dropped.

But amid the stress of a losing campaign and at risk of losing Dykstra’s Ontario seat, Stephen Harper opted to keep him on the ballot.

Days later, Dykstra was accused in media reports of buying drinks for underage girls at a nightclub, but he was still kept on.

“A campaign operates like a pressure cooker and the kind of frenetic pace of it all clearly shows there was some divide amongst senior leadership in the campaign over what to do,” says Conservative strategist Jamie Ellerton.

Still, Ellerton argues, “perhaps more questions should have been asked at that point and (going) forward to ultimately make the decision about Mr. Dykstra's candidacy.”

Harper issued a statement Friday saying he didn’t have enough information on allegations against Rick Dykstra to justify blocking his candidacy in the 2015 federal election campaign.

“When allegations were brought to my attention during (the) 2015 election campaign, I understood the matter had been investigated by the police and closed a year prior,” Harper wrote in the statement posted to Twitter.

“Given this understanding of the situation, I did not believe that I could justify removing him as a candidate,” Harper went on.

“Recently, much more information has come to light, including information to the effect that the original investigation may not have been complete,” the former prime minister said.

Novak, Harper’s chief of staff, made people sign anti-harassment policies when they joined the Prime Minister’s Office. He also made them go through regular training. He says he now believes Dykstra should have been fired.

“This was an extremely difficult decision that ultimately turned on whether a closed investigation without charges was sufficient grounds for firing,” Novak said.

Meanwhile, questions remain about how and why the Conservatives determined the investigation was closed.

Senior sources say Harper and Novak assumed police had closed the investigation because they found no basis for criminal charges.

Sources point out that Harper had no tolerance for excessive partying or sexual misconduct, insisting the decision to keep Dykstra on was based primarily on the termination of the investigation and absence of criminal charges.

New information is raising the possibility that the alleged victim withdrew her complaint, rather than the police concluding there was nothing behind the allegations.

Pollster Nik Nanos says the situation shows the need for “more ethics and values in politics related to what is appropriate behaviour and what is not appropriate behaviour.”

Dykstra has denied the allegations against him reportedly made by a former staffer in 2014, and they have not been tested in court.

Federal Conservative Leader Andrew Scheer has said there will be a third-party investigation into how Dykstra was allowed to run in 2015.

Dykstra lost in that election but went on to become president of the Ontario Progressive Conservative party, until his resignation last month.

With a report from CTV’s Mercedes Stephenson in Ottawa