Irishman Enda McLaughlin who went on a stabbing frenzy in Germany before being knocked down by a car and killed thought he was a character in a South Park, his sister has said.
Mr McLaughlin's family believe that he never got the help he needed to deal with his mental health issues, despite several stints in prison.
The 27-year-old died when he was hit by a car being driven by a British couple near the German town of Acchen.
Earlier on Monday morning he stabbed a Dutch taxi driver who had driven him over the border from Holland.
Minutes later he stabbed a 49-year-old pedestrian when he refused to hand over money.
When a second taxi driver left McLaughlin at a motorway service station, the Donegal man stabbed an Estonian lorry driver before being knocked down on a road nearby. He died at the scene.
Speaking at the family cottage in the townland of Glentogher, 4km from Carndonagh in Co Donegal, his family said they were devastated by his death.
"He just never grew up. He was like a child," his sister Catherine (32) told the Irish Independent.
"Our mother left when he was three. I don't think he ever got over that and suffered from separation anxiety. He had been diagnosed with bipolar disorder.
"Enda thought life was a cartoon and he was in it. He thought he was a character in 'South Park', that's just the way he was.
"He would do worse and worse things and each time he thought it was fun. He got in with people who thought what he did was funny."
She said her pleas to the authorities to have him sent to the Central Mental Hospital in Dundrum fell on deaf ears.
"He would come back out of prison worse than before. People in there would dare him to do things and he would come out and he would do it.
"That's why he told a judge who asked him what he should do to him that he should be shot. He wanted to be shot."
Neighbours in the tight-knit community were rallying around the family yesterday.
Catherine says they wouldn't be mourning if "the system" dealt with mentally ill offenders better.
"Treatment would have served him and society better. Our health and justice ministers need to wake up to the mental health crisis in this country or we will have more cases like this," she said.
The grieving sister said Enda wasn't always in trouble.
"He worked as a plasterer and he would work away for a few months and then he'd break again, through drink or drugs or whatever," she said.
"He was a genuine guy; he was funny and there would be silence in the house when he sang, he was that good.
"He just never grew up. He was a child, it's just tragic what has happened in Germany, so tragic for everyone but Enda should never have been allowed to get to that stage and his life has been lost now.
"Our only consolation is that he's in a better place now. I know he's in a better place."
Her father Patrick said gardai had called to his home to inform him of Enda's death.
Local TD Charlie McConalogue was helping last night to get more information from the German authorities to help bring the body of Enda McLaughlin back to Ireland. A post mortem was being carried out in Germany last night.