BRAMPTON, Ont - The prosecution in a high profile terrorism case effectively branded its own star witness a liar Wednesday, accusing the RCMP informant of deliberately changing his testimony to protect the young accused on trial.

The witness, Mubin Shaikh, rejected the suggestion but conceded he didn't believe that a group of Toronto-area teens caught up in the alleged plot to cause horrendous bloodshed in Canada should be prosecuted as terrorists.

"I did see myself as a protector of the vulnerable," Shaikh said under cross-examination by Crown lawyer John Neander.

Court has heard that the leader of the alleged conspiracy wanted to carry out truck bombings, storm Parliament Hill, and behead politicians.

But Shaikh maintains the man deliberately kept the accused -- who has pleaded not guilty -- and other associates in the dark about his horrific plans.

The Crown lawyer produced statements Shaikh had made in previous hearings and accused him of "inconsistencies" in three key areas of his testimony.

For example, Neander accused the witness of changing his story about what the teens were told when they were ordered to clean up before leaving a winter camp north of Toronto they attended in December 2005.

In prior hearings, Shaikh said the youths were told the clean-up was to hide evidence of terrorism training. At trial, he testified the youths were told the clean-up was to protect animals and the environment.

While Neander stopped short of asking the court to declare the married father of four a hostile witness, his frustration was obvious.

"I can hear you fine from over there," Shaikh said at one point as the normally low-key Neander raised his voice.

"Every fibre of your being as a loyal Canadian and a devout Muslim recoiled at what (the leader) was doing to corrupt them, isn't that correct?" Neander asked.

"Yes," Shaikh replied.

"That's why now you maintain this incorrect pretext that there was some effort . . . to mislead the youths as to the purpose of the cleaning up the camp."

Shaikh stuck to his guns, much to the satisfaction of the defence, which has taken pains to portray the youths as dupes who had no real idea of what was going on.

"The Crown appears to be suggesting that you see yourself somehow as the protector of these young people, these vulnerable young people, and would therefore defy the oath that you took to tell the truth," said defence lawyer Mitchell Chernovsky.

"I seek refuge with Allah for such an implication," Shaikh retorted.

"So you stand by your evidence that whatever reason (the leader) had, whatever tracks he was trying to hide, whatever damage control he was trying to do, he told those kids they were cleaning this place up to protect the animals?"

"That's correct."

Shaikh was instrumental in helping police bust what they described as a homegrown terrorist conspiracy two summers ago.

As such, his evidence is crucial to the prosecution's position that the 20-year-old man on trial knew he was involved in a terrorist plot.

The accused, who was 17 at the time of his alleged offences, is the first of 11 people still charged to stand trial and Shaikh's evidence is likely to be prominent in all those trials as well.

In allowing Neander to do the cross-examination of his own witness, Ontario Superior Court Justice John Sproat agreed there were inconsistencies between what Shaikh said during the trial and what he had said previously.

The trial resumes Thursday, with the Crown expected to play a videotaped statement the accused gave to police.