Gary Mattson, shown on a security video before attacking Tom Bregg, was declared a dangerous offender Monday. (Edmonton Transit)

An Edmonton man who viciously attacked a city bus driver in 2009 has been declared a dangerous offender.

The designation by provincial court Judge Harry Bridges means Gary Mattson will remain in prison until it's determined he is no longer a risk to the public.

Driver Tom Bregg was not in the court Monday when the judge delivered his decision.

"The injuries to him were devastating," said prosecutor Patricia Innes. "From his disfigurement, to the effect on his eyesight, to obviously the impact on his ability to carry on life as he knew it, from enjoying life."

Innes said she wasn't surprised by the judge's decision.

"In practical terms, the judge not only made the finding that he's a dangerous offender, but also that he should serve an indeterminate sentence, which means that Corrections Canada now has custody of this gentleman until he is of a low risk to return to the community."

Mattson pleaded guilty in May 2010 to aggravated assault for attacking Bregg on his bus during the morning rush hour on Dec. 3, 2009.

Bregg had tried to remove Mattson, who was heavily intoxicated and refused to pay the $2.50 fare, from his city bus.

Tom Bregg speaking to reporters in Ottawa last March, has not returned to work. CBC

Mattson punched Bregg in the face, pulled him off the bus and stomped on his face 15 times. The attack put Bregg in intensive care for two weeks and left him with brain injuries and blind in one eye.

"(Gary's) the last person who would attempt to defend or justify or excuse or minimize what happened," said his lawyer Naeem Rauf.

Rauf believes public outrage over the attack played a role in the judge's decision.

Mattson's previous criminal record contains a few assaults, none requiring medical attention and his longest sentence was 90 days, he said.

"So how you can leap from that to calling him a dangerous offender completely mystifies me. He's been treated in this process like a specimen in a dissecting room," said Rauf.

"The people who treated him as a whole human being ... saw a real humanity in him."

Rauf said he will encourage Mattson to appeal.

Mattson cried silently in the prisoner's box and appeared to be angry when the judge sent him to jail indefinitely.

Bregg has not returned to work since the attack. He's still fighting for benefits with the Worker's Compensation Board, said the Amalgamated Transit Union.