Omar Khadr's apologetic tone didn't seem to move Stephen Harper much Friday as the prime minister defended his Conservative government's efforts to keep the former Guantanamo Bay prisoner behind bars.

"Mr. Khadr, as we all know, pled guilty to very grave crimes, including murder," Harper told a news conference as he offered his thoughts and prayers to the family members of U.S. Sgt. Christopher Speer.

"Our government's priority in these matters is always to make sure, first and foremost, we keep in mind the protection and security of the Canadian population."

Harper said little else, citing the fact the matter remains before the courts.

Khadr, now 28, pleaded guilty in October 2010 before a widely discredited military commission to five war crimes — including murder in the death of Speer, a U.S. special forces soldier.

On Thursday, he walked free after an Alberta judge rejected the government's last-ditch attempt to block his release, saying they had failed to prove Khadr posed a risk to the public or could do harm to Canadian interests.

'Give me a chance'

Some hours later, during a remarkable news conference on his lawyer's Edmonton driveway, Khadr apologized for the pain he's caused and urged Canadians to give him a chance to demonstrate his worth.

Omar Khadr spoke to the media in Edmonton Thursday evening, and said he is 'better than the person' Stephen Harper thinks he is. (CBC)

"I will prove to them that I'm more than what they thought of me, I'll prove to them that I'm a good person," Khadr said.

"Give me a chance — see who I am as a person, not as a name — and then they can make their own judgment after that."

Khadr spent almost 13 years behind bars — four of them as a convicted war criminal.

He was captured, badly wounded, by American forces in Afghanistan in July 2002, when he was 15 years old. At one time, he was the youngest prisoner at the American prison compound in Guantanamo Bay.

After his release on bail, he offered a comment on Harper's hard-line stance: "I'm going to have to disappoint him, I'm better than the person he thinks I am."

Justice Minister Peter MacKay sounded a slightly more conciliatory note than his boss Friday, saying Khadr's public declaration that he had renounced violence was a good first step after his release from prison.

MacKay, speaking at an event in Halifax, said people shouldn't lose sight of the fact that Khadr was involved in terrorism.

"What I hope will happen is that Mr. Khadr will abide by Canadian laws, respect people's safety, and he is now is a position where he is going to be given that opportunity to prove that," he said.

"Let's look ahead with optimism, but with caution, when it comes to individuals who have past proven tendencies that have resulted in the loss of human life."

After Khadr's release, a spokesperson for Public Safety Minister Steven Blaney said the minister regretted that a convicted terrorist had been released without having served his full sentence.

Khadr's release came with a list of restrictions, including wearing a tracking bracelet and a curfew.