Allan Chamberlain began his evidence on Wednesday in the case against Domenic Perre, 63, who has pleaded not guilty to the murder of Detective Sergeant Geoffrey Bowen and the attempted murder of lawyer Peter Wallis in the 1994 attack.

His appearance came after lengthy argument over access by defence counsel to a diary kept by Mr Chamberlain's mother around the time of the incident.

In his early testimony, Mr Chamberlain was taken through his family background in some detail.

He also told the court of how he had a business at one stage, selling such things as body armour which was imported from the United States.

He said on one occasion he sold 22 bullet-proof vests to police after demonstrating their effectiveness by taking an officer's handgun and shooting himself in the chest.

Prosecutors are expected to use Mr Chamberlain to link Perre to the parcel bomb used in the NCA blast while his defence is expected to argue there is no such link on the available evidence.

Perre's defence team previously told the court he was "explicit" in proclaiming his innocence both immediately after the bombing and in relation to the charges he currently faced.

But the prosecution has alleged the bombing of the NCA office was a personal attack on Sgt Bowen.

In the Crown's summary of the case, Sandi McDonald SC said Perre's hostility towards the detective had grown because of their interactions following the seizure of a multi-million-dollar cannabis crop in the Northern Territory in August 1993.

"The bomber intended that the parcel bomb travel through Australia Post and end up in the hands of Bowen and that when he opened it his body would suffer the full force of the explosion," Ms McDonald said.

The trial has also heard how Sgt Bowen was found slumped among the debris as flames and smoke continued to engulf the NCA headquarters immediately after the bombing.

Former police officer Michael Schultz, who was among the first on the scene, told the court there was "lots of mess" with desktops, ceiling panels and office furniture piled up, but when they removed some of the debris they found the detective.

"From my perspective, I was hoping he was alive and I was trying to talk to him and reassure him and encourage him to hang in there," Mr Schultz said."

But as Sgt Bowen was turned, he saw that his left arm was missing from beneath the elbow and that his left trouser leg was shredded with bits of flesh showing through.

Sgt Bowen died from his injuries while Mr Wallis lost an eye and was severely burnt.

The trial was continuing before Justice Kevin Nicholson who is sitting without a jury.

Australian Associated Press