Napier gunman Jan Molenaar - who died of a single self-inflicted gunshot to the head - made a makeshift bulletproof vest.
Police investigation head Detective Superintendent Rod Drew said Molenaar's autopsy was completed in Wellington yesterday.
The pathologist found the cause of death as being a single gun shot wound to the head. There was no evidence the gunshot was fired by police or any other agency, Mr Drew said.
Molenaar shot and killed Senior Constable Len Snee during a routine search of his home. He also shot and injured Senior Constable Grant Diver, Senior Constable Bruce Miller and civilian Leonard Holmwood.
In an unusual move, Coroner David Crerar today released a special minute - with the approval of family - to allow the cause of Molenaar's death to be released.
It said all information presently available indicated Molenaar's fatal gunshot wound was self-inflicted.
Mr Drew has also revealed that Molenaar wore a leather motocross style vest during the seige.
A metal sheet was found on the bed after his death. Mr Drew said it was thought Molenaar fashioned this over his front, "which no doubt was intended as a bullet proof vest".
"I think it's certain these garments were manufactured long before this took place," Mr Drew said.
"There is just enormous damage inside this house, you just can't imagine what it looks like."
Meanwhile, Mr Diver's condition is improving and he will be attending Mr Snee's funeral today. Mr Miller is still in ICU but improving. Mr Holmwood has gone to theatre today to try and remove shrapnel; he is still in ICU but improving.
Bullet damage had been found to houses up to 400 metres away from Molenaar's home. Mr Drew said there was evidence to support up to 21 attempted murder cases, where shots had been fired at neighbours, emergency services and police.
Mr Drew said the investigation had been very difficult.
"Many of us knew Lenny well; many of us knew him very well.
"So it's been very hard, I feel very proud of them all because they've shown real grit in getting on with it all. "