TORONTO - A youth accused of being part of an alleged homegrown Islamic terrorist plot to behead the prime minister, attack Parliament and cause widespread mayhem is expected to learn Thursday whether a judge agrees with the charges.

Ontario Superior Court Justice John Sproat is slated to render a verdict in the first of the so-called "Toronto 18" cases to go to trial, a decision which could have implications for the coming prosecutions of the 10 remaining suspects.

Lawyer Dennis Edney, who represents one of the alleged plot leaders, said Wednesday that much will depend on how credible Sproat found paid informant Mubin Shaikh, the government's key witness.

"If the judge finds him not credible, then that really has severe impact for the Crown's case in the adult cases," Edney said.

"Mr. Shaikh's role in guilt or innocence is quite critical."

Beyond judging the reliability of the enigmatic RCMP informant, the key decisions for Sproat will be whether the plot was a real threat or just a "jihadi fantasy" dreamed up by braggarts who talked an ugly game but had no real intention, nor ability, to carry out their bloody schemes.

If he concludes the conspiracy was real, his verdict then turns on whether he believes the accused was a willing and knowledgeable participant, or simply a troubled teen who had no idea of what the group was really up to, as Shaikh maintained during his testimony in a Brampton, Ont., court.

The 20-year-old accused cannot be named because he was 17 at the time of his alleged offences 2 1/2 years ago.

He pleaded not guilty to participation in a terrorist group and aiding a terrorist group by shoplifting camping supplies and walkie-talkies.

In the summer of 2006, an intense investigation involving Canada's spy agency and the RCMP ended with the arrests of 18 people in the Toronto-area and the seizure of apparent bomb-making materials.

The suburban courthouse at which the suspects were arraigned swarmed with assault-rifle-toting police and dozens of reporters and cameras.

Since then, however, seven of the accused - including three other underage suspects - have seen their charges dropped or stayed amid determined defence efforts to portray the allegations as vastly overblown.

"When the first details came out, it had the flavour of enthusiasm and a lot of young male testosterone at work," said David Charters, a University of New Brunswick professor and former member of the Advisory Council on National Security to the federal cabinet.

"What I didn't see was a coherent plan. Maybe it will come out more clearly in subsequent trials."

Trial dates have not yet been set for the 10 adult suspects.

At the youth's trial, which wrapped up Aug. 8, prosecutors insisted the accused - a Hindu convert to Islam - might have initially been in the dark about the nefarious plot to "cripple" Canada.

But Crown lawyer John Neander argued the youth must have come to learn of his mentor's horrific plans and would have helped execute them.

Neander made much of the teen's enthusiastic attendance at two camps in Ontario in December 2005 and May 2006.

The prosecution maintains the camps were for terrorist training - based on evidence participants marched, played paintball games, shot a 9-mm handgun, and heard lectures on waging war on the West.

But defence lawyer Mitchell Chernovsky portrayed the camps as a religious retreat.

His client, he argued before the court, was a "naive and immature" teenager whom the alleged plot leaders deliberately kept in the dark about a scheme he denounced as sheer fantasy.

"He didn't know of any plans to attack Canada," Chernovsky said in closing arguments. "He said that repeatedly, he said that sincerely, and he said that quite credibly."

Shaikh's agreement with that view prompted prosecution suggestions he was changing his evidence to help the accused.

Court heard the "polite and respectful youth" was estranged from his family and sought out other Muslims - one of whom, the charismatic alleged co-leader of the terrorist ring, became his mentor and friend.

His parents sat quietly in court through much of the trial, which began hearing evidence in June.