"I don't think we have enough evidence to use that word," Mulcair said at the end of an emotional party caucus meeting Wednesday, one week after Michael Zehaf Bibeau opened fire on a soldier and then on security guards just outside the government and Opposition caucus meeting rooms.
"When you look at the history of the individual involved, you see a criminal act, of course," he added.
"But . . . I think that we're not in the presence of a terrorist act in the sense that we would understand it."
Mulcair's comments were met with immediate condemnation from Conservatives and the leader of the Liberal party.
"The RCMP was clear, these were acts of terrorism, (so) these were acts of terrorism," said Justin Trudeau.
"It's ridiculous," added Conservative MP Peter Kent.
"It was clearly an act of terror (based on) his background and motivation. RCMP Commissioner Bob Paulson's remarks about his motivation I think are very clear."
The remark re-emphasized a stark ideological divide in the House of Commons about how to react to the deaths of two Canadian soldiers last week.
Mulcair said it's obvious that Zehaf Bibeau had mental issues, and that his actions in killing a soldier at the National War Memorial and firing on security on Parliament Hill were reprehensible.
But Mulcair said the latest information about the lone shooter indicates he should be defined merely as a criminal.
He later seemingly clarified his comments in the House of Commons, referring to the differences between a criminal act carried out by someone with a history of mental issues and an act of terror carried out by an "organized" individual or group.
Still, Wednesday's message was a carry-over from earlier in the week, when Public Safety Minister Steven Blaney warned that, while the government doesn't want to over-react to last week's events, it's time to stop "under-reacting" to the threat of terrorism.
Canada's Criminal Code defines terrorism as an act committed "in whole or in part for a political, religious or ideological purpose, objective or cause" with the intention of intimidating the public.
MPs of all stripes were reflective Wednesday on the events of a week ago as they attended their regularly-scheduled party meetings with some saying they were having a difficult day recalling the mayhem.
The NDP brought a counsellor into the party's caucus room, just in case anyone wanted to talk about the trauma they experienced.
Zehaf Bibeau shot and killed Cpl. Nathan Cirillo at the National War Memorial on Oct. 22.
A funeral for the 24-year-old Hamilton native was held on Tuesday.
Minutes after killing Cirillo, Zehaf Bibeau rushed through the front doors of Parliament's Centre Block, where he was eventually fatally subdued in a hail of gunfire that involved RCMP officers, security and the Sergeant-at-Arms of the House of Commons.
Almost immediately after the mayhem began, Conservative MPs were posting comments on the Internet, referring to a "terrorist attack."
The mantra stuck in government circles, and was later voiced by the RCMP and on Tuesday by visiting U.S. Secretary of State John Kerry.
The Harper government is considering ways to beef up anti-terrorism laws, including whether to introduce legislation that would prohibit terrorists or their sympathizers from using the web to promote their causes.
Justice Minister Peter MacKay confirmed to reporters Wednesday that the government has held broad discussions with officials within the justice and public safety departments with an eye toward finding new ways to prevent the promotion of terrorism online.
“There’s no question that the whole issue around radicalization and the type of material that is often used that we think is inappropriate, and we think quite frankly contribute to – again this is my word – the poisoning of young minds, that this is something that needs to be examined," MacKay said as he entered the caucus meeting.
MacKay emphasized that any new or bolstered existing measures would include checks and balances to ensure judicial oversight over the forceful removal of online material that could be seen as contributing to the "proliferation of terrorism."
Privacy watchdogs issued a joint statement Wednesday, calling on the Harper government to ensure that any new measures adopted are proportionate.
The statement from 15 privacy and information commissioners voiced concerns that new powers given to police could infringe on privacy rights and civil liberties.
"We acknowledge that security is essential to maintaining our democratic rights," the commissioners wrote, calling on Ottawa to ensure effective oversight of any new laws.
"The response to (terrorist) events must be measured and proportionate," they said.
"Canadians both expect and are entitled to equal protection for their privacy and access rights and for their security," said the statement.
MacKay suggested that some tweaking could also be coming for measures that have already been introduced, including Bill C13, ostensibly an anti-cyber bullying bill that could be used in terror investigations.
The minister also referred to Bill C44, introduced Monday, which would see Canada's spy agency, the Canadian Security Intelligence Service, given new powers to conduct surveillance outside Canada and share information with other national governments.
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