Key Points:

The Department of Corrections "stuffed up" in its handling of convicted murderer Antonie Dixon, who died in prison overnight, his lawyer said this afternoon.

Corrections this morning confirmed media reports that Dixon died in Auckland's Paremoremo Prison, apparently of self-inflicted injuries.

In January 2003, Dixon attacked two women, Simonne Butler and Renee Gunbie, with a samurai sword, severing or partly severing their hands in the small settlement of Pipiroa near Thames.

He then continued his P-fuelled crime spree, driving to Auckland where he shot dead James Te Aute.

During his trials his defence argued he was insane, but the Crown countered that he was "not mad, but bad".

Dixon's lawyer Barry Hart today said when he had spoken to his client this January, he had a sense his mental health was deteriorating fast.

Mr Hart said his client refused to take his medication and had been beaten up several times by inmates.

He said Dixon had been transferred between prisons without his lawyer's knowledge and should have been put in a psychiatric unit, not a prison cell.

Dixon was recently understood to have tried to pull a makeshift weapon on Mr Hart during a prison visit.

The Sunday News reported that prison staff were forced to intervene after he pulled the weapon out of his shoe.

Dixon was due in the Auckland High Court this morning for a case management hearing.

Auckland prison assistant general manager of operations, Leanne Field, said staff tried to revive Dixon overnight but he was pronounced dead by ambulance staff.

"The Department is now undertaking an initial investigation to determine what happened. However, I can say that it appears Dixon died of self-inflicted injuries," Ms Field said.

She said a Coroner's investigation by police was under way. An investigation by the prison inspectorate will also be carried out.

Dixon was first convicted in 2005 of murder, grievous bodily harm, firearm charges, shooting at police.

The Court of Appeal later quashed the conviction, ruling the summing up by Justice Judith Potter contained major errors of law.

In August last year, after a second trial by a jury in the High Court in Auckland, Dixon was again found guilty on the eight charges he faced.

Details about his upbringing emerged during his trials, including alleged sexual abuse on him as a child and incidents of him being kept outside tethered to a clothesline.

He was remanded in custody for sentencing early this year.

Mr Hart said in December that Dixon would be appealing his conviction and seeking a third trial following his sentencing.

In December 2007 Dixon used a fork to try to gouge out the eye of a fellow prisoner who required hospitalisation.

It was later discovered Dixon had his own MySpace web page with comments about his crimes and photos of him in prison on it.