Carleen Bryant spoke about her son on Channel 9's 60 Minutes on Sunday night, where she was asked what her dead husband, Maurice, would have thought of the Port Arthur murders that her son was convicted of.

"Well, I don't believe it would have happened," she answered.

Martin Bryant entered the Broad Arrow cafe at the historic Port Arthur site where he opened fire and killed 35 people on April 28, 1996.

He is serving 35 life sentences in Risdon prison.

His mother, who is the only person who visits Bryant, admitted that he was an "annoying" and "different" child.

She said that she often found Bryant's toys broken and didn't know if it was through temper or frustration.

Although his mother still doesn't believe he was capable of abusing people she says he became unpleasant towards his sister Lindy's friends.

"I'm his mother, I know what he was like. Yes he was annoying like most boys are especially with their sisters but, as he got older and Lindy started bringing new friends home, he started turning very nasty towards them.

"He'd just shout at them and tell them not to ring any more and abuse them if they came there to the house," she said.

Bryant was diagnosed with Asperger's syndrome three years ago and is overweight from medication and lack of exercise.