Zakaria Amara, 24, has been sentenced to life in prison for his role in a plot to bomb the Toronto Stock Exchange and two other high-profile targets. (CBC)

The main organizer of a plot to set off three massive bombs at the Toronto Stock Exchange and other high-profile targets in Ontario was sentenced Monday to life in prison.

Zakaria Amara's sentence is a message of deterrence to society, Ontario Superior Court Judge Bruce Durno said in a Brampton court. If Amara's plan had been successful, "it would have terrorized Canadian society and killed many," the judge said.

Amara, one of the so-called Toronto 18, pleaded guilty in October 2009 to knowingly participating in a terrorist group and intending to cause an explosion for the benefit of a terrorist group.

Zakaria Amara is shown in a sketch at his court sentencing on Monday in Brampton, Ont. (Alex Tavshunsky/CBC)At the sentencing hearing, Durno gave Amara two days' credit for each day he had served in pre-trial custody, equal to seven years and three months.

Upon hearing the sentence, some of Amara's female relatives and supporters began to cry.

Amara, 24, then addressed the court and vowed to reform himself.

Helper also sentenced

Earlier in the day, Durno sentenced one of Amara's accomplices, Saad Gaya, 22, to 12 years in prison.

Gaya pleaded guilty to belonging to a terrorist group and intending to cause an explosion. He was among 18 men and youths rounded up in 2006 and charged in what's known as the Toronto 18 terror plot.

Videotape shows authorities arresting two members of the so-called Toronto 18 as they unloaded what they believed were large quantities of ammonium nitrate. (CBC)Gaya has been in custody since his arrest and with 7½ years credit for the time he has already served, Gaya was sentenced to serve another 4½ years, but could be eligible for parole in 1½ years.

Gaya was described in a psychiatrist's report as a sheltered young man — he was 18 at the time of his arrest — who was naive, immature and lacking in "street smarts." Still, he is an intelligent young man who could have put two and two together, the judge said.

"While the offender did not know how big the bombs were going to be … he was wilfully blind as to the likelihood that there would be death or serious bodily harm," Durno told a packed courtroom.

"His degree of responsibility remains relatively high, albeit not as high as the others in the plot."

The plan was to set off one-tonne ammonium nitrate bombs at three targets: the Toronto offices of Canada's spy agency, CSIS, the Toronto Stock Exchange and a military base in eastern Ontario.

The Oklahoma City bombing in 1995 that killed 168 people used one tonne of ammonium nitrate.

Durno condemned the "chilling and terrifying" plot that surely would have resulted in mass deaths and destruction.

Saad Gaya, shown in a sketch, pleaded guilty to belonging to a terrorist group. (Alex Tavshunsky/CBC)

The RCMP hailed the verdicts as a "successful conclusion" to "a long and complex investigation involving several agencies, both domestic and international."

"This … demonstrates that the appropriate response to terrorism lies with good intelligence, integrated law enforcement and effective prosecutions," Gilles Michaud, the assistant commissioner of the RCMP's National Security Criminal Investigations unit, wrote in a news release.

But it "also underscores the reality that Canada is not immune to the threat of terrorism," Michaud wrote.

"Rest assured, the RCMP and its law enforcement and intelligence partners will remain diligent in continuing to investigate to the fullest extent all threats to Canada's national security."

Gaya has made strides to rehabilitation: judge

At his sentencing hearing last month, Gaya told the court he was "extremely grateful" the scheme "did not progress any further." Gaya said he didn't want to be branded a terrorist and that he didn't know the intended targets were the stock exchange and CSIS.

"His prospects to reform himself and to stay away from the ideology that led him into criminal conduct are very good," Durno said.

"I am persuaded that with counselling, the offender can be rehabilitated and become a law-abiding member of society."

Gaya's lawyer said he disagreed with the judge's characterization of Gaya as "wilfully blind" and had been hoping for greater credit for Gaya's pre-trial custody, given that about one year of it was served in segregation.

"Terrorism is a heinous and evil crime, but not necessarily everyone who commits a heinous and evil crime is himself evil," Paul Slansky said outside court.

"I don't believe Mr. Gaya is evil. I do believe that he was a misguided youth who made some seriously erroneous mistakes in deciding to trust these people, who were themselves misguided."

Gaya and Saad Khalid, who was sentenced to 14 years but given seven years' credit for pre-trial custody, were arrested while unloading a delivery truck filled with what they thought were three tonnes of ammonium nitrate.

A psychiatric assessment found no evidence Gaya poses a significant risk in the near future, but based on his past behaviour, "risk over the long-term period cannot be ruled out."

Durno said that assessment cannot be ignored, but that Gaya has already made strides toward rehabilitation, and strong family and community support will help toward that goal.

Gaya has taken correspondence courses while in custody, his family and friends have put more than $60,000 in an educational trust fund for him, and the judge received three letters offering Gaya immediate employment upon his release from prison.

In his post-arrest interview Gaya said the goal of the explosions was to pressure Canada to withdraw its troops from Afghanistan. The former McMaster University science student was the only one of the 18 people arrested to give a statement to police.

Of the 18 people arrested in 2006, four have pleaded guilty, seven have had their charges dropped or stayed, a youth was found guilty, one man's trial began last week and five others face a trial in March.

With files from The Canadian Press