TORONTO - A man police once suspected of planning to bomb the tumultuous G20 summit in Toronto was obsessed with explosives and became increasingly sympathetic to anarchists, his trial heard Thursday.

In closing submissions, the Crown portrayed Byron Sonne as someone who wanted to "stick it to the system" and spent "a great deal of effort, time and money" to do so.

Prosecutor Liz Nadeau conceded the case against Sonne, 39, was "circumstantial" but said the Crown didn't have to prove the accused actually planned to bomb anything, just that he planned to make explosives.

"He had the chemicals for that purpose," Nadeau told Ontario Superior Court Justice Nancy Spies. "He wanted to have the components."

Sonne, who is charged with four counts of possessing explosives and one of counselling to commit mischief, has maintained the array of legal chemicals found at his upscale Toronto home were for his model-rocket hobby and making crystals.

But Nadeau suggested his hobby was a belated ruse to disguise more nefarious intent.

"If you're going to build your own rocket, would you start with the fuel?" she said.

"What's the use of joining a rocketry group unless he needed a cover? He still didn't have a rocket."

Nadeau outlined the extensive list of chemicals seized from his home along with recipes for making home-made explosives.

The chemicals included various acids, dozens of hexamine fuel tablets and ammonium nitrate -- a common fertilizer -- as well as ordinary household substances such as paint-thinner and drain cleaner.

"I wish I'd taken chemistry instead of physics," Spies quipped at one point.

Computer records show Sonne, who had laboratory devices and electronic bits and pieces, did extensive research on explosives, and was "fascinated by explosions," Nadeau told the judge-only trial.

The prosecutor reminded the court of evidence that Sonne had engaged in numerous Internet chats about summit security measures, including sharing plans to listen to police scanners.

He posted advice on how to scale a security fence and pictures of surveillance cameras set up in advance of the summit in June 2010.

"Some cameras may be easy to interfere with. Checking," he said in one of numerous tweets.

The judge noted there were widespread concerns about the extensive security implemented downtown, including a two-metre metal fence, aimed at protecting G20 leaders.

But Nadeau suggested Sonne could simply have gone to the authorities if he had concerns about the security measures if, as he maintains, he was "testing the system and exposing vulnerabilities."

Sonne, she said, went from being "irritated with protesters" and supporting Prime Minister Stephen Harper to becoming an anarchist.

He also had a "fascination, bordering on obsession, with guns," Nadeau told court, as Sonne's parents and numerous supporters looked on.

The self-described security geek and Internet security expert was arrested just days before the summit began. The G20 weekend saw police arrest more than 1,000 people following a wave of vandalism that included police cars set ablaze.

Police accused him of having homemade explosives, and of inciting others to tear down the security fence and surveillance cameras through his Twitter and Flickr accounts.

The Crown previously dropped five other charges, including mischief, possession of a dangerous weapon and intimidating a justice system participant.

Sonne spent 330 days in jail before being released from custody on bail last May.

The defence, whose only witness was a rocketry enthusiast, argues Sonne might have had numerous if strange interests but no criminal intent. It makes its closing submissions on Friday after the Crown wraps up.