Julian Leslie Yeaman appeared via video link in the ACT Supreme Court on Thursday when Chief Justice Helen Murrell delivered her verdict of guilty to an act of arson.

He had pleaded not guilty on the ground of mental impairment and faced a judge-alone trial in September.

Chief Justice Murrell's judgment states that Yeaman was a detainee at the Alexander Maconochie Centre in October 2019 when he covered a vent in his cell that was designed to detect smoke.

He then used a lighter, which he was entitled to have, to ignite a cardboard box containing linen and a mattress.

Once the fire began, he used an intercom to call for help, saying words to the effect of "I have lit a fire, I've done it".

"Come and help me," he said.

The fire triggered a code red among corrections officers who had to extinguish it before evacuating other detainees.

ACT Fire and Rescue attended to help contain the situation.

Yeaman, while in a clinical room, later said he was "willing to go out with a bang" and asserted that he was "fit to plea".

During a police interview, the 38 year old said he would "rather die than have to put up with the life and the existence I'm bound to live by for the rest of my life".

"I just got a lighter and burnt the place. Grabbed a bunch of stuff, burnable stuff, and burnt it," he said.

He also stated that he wasn't trying to kill himself or burn himself alive.

MORE NEWS

In her judgment, Chief Justice Murrell said the defendant "intended that the fire would cause damage" and that his behaviour was "not the actions of someone who does not know the nature and quality of their conduct of lighting a fire".

Chief Justice Murrell said that while Yeaman was suffering from mental impairment and that his ability to control his impulses were significantly reduced, he was still able to control his behaviour generally.

She said that the impairment meant he had difficulty rather than him not being able to control his conduct.

"He undertook the conduct because it was wrong, and it would therefore attract attention to his plight, operating as protest against the extent to which others controlled his life," she said.

"I am satisfied beyond reasonable doubt that the accused knew the nature and quality of his conduct and there is no reasonable possibility that he did not know [of that conduct]."

The defendant also faced other charges from a separate incident in which he was found not guilty.

He will be sentenced on October 28 for the arson.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: