A police informant who was paid $4.1 million to infiltrate the so-called "Toronto 18" terror group described accused bomb plotter Shareef Abdelhaleem as an "aggressive person" on the first day of his trial.

Abdelhaleem, 34, is charged with participating in a terrorist group and intending to cause an explosion. He pleaded not guilty to both counts.

His trial -- by judge alone -- is taking place at a well-guarded courthouse in Brampton, Ont.

The Crown's star witness, police informant Shaher Elsohemy, said he met Abdelhaleem at an Islamic school in Mississauga. The two were friends, Elsohemy said, until Abdelhaleem went to police on suspicion that Elsohemy's brother shattered the windshield of his BMW.

"He was pretty aggressive in describing what he would do," Elsohemy testified in court Monday. "At that time I had to end the whole (friendship) because the threats were increasing and it made no sense to me whatsoever."

The accused also spoke of jihad, and saying that he was "playing around with the idea of going back home for the ultimate duty," Elsohemy told the court.

The Crown was expected to present the accused as a key player in the plan to bomb the Toronto Stock Exchange and other landmarks in Canada's biggest city. CSIS, Canada's intelligence agency, was also said to be a target in the attack.

Authorities say the attack was planned as a way to pressure the Canadian government into withdrawing troops from Afghanistan. It was foiled when police arrested 13 men and five youths in a 2006 raid.

The suspect, who earned a six-figure salary as a computer programmer, has said he is innocent of the charges and has accused the police of entrapment.

Abdelhaleem's lawyer, William Naylor, said outside of court that he will raise the large sum paid to the informant in his defence of his client.

"A $4.1-million payoff for this is pretty steep," Naylor said. "It's unprecedented in Canada as far as I understand."

He suggested Elsohemy was more interested in money than the truth.

Elsohemy entered the Witness Protection Program more than three years ago and hadn't been seen since.

Abdelhaleem is one of 18 people who were arrested and charged in 2006 with participating in the alleged terror plot. He is the first to be tried as an adult.

Most of the accused were charged with attending a training camp, but seven of the 18 people arrested have since had their charges dropped or stayed.

Three people have pleaded guilty to the charges and one man was convicted in court of participating in and contributing to a terrorist group.

Seven others, including Abdelhaleem, remain in custody and are awaiting trial.

With a report from CTV Toronto's John Musselman