As the Crown opened its case in the retrial of Mr Eastman for the alleged assassination of Colin Winchester, the ACT Supreme Court jury heard the former public servant came to develop a "murderous hatred of police".

On January 6 that year, prosecutors said, Mr Eastman said the police should be taught a lesson.

"The Crown case is that Mr Eastman did teach police a very harsh lesson just four days later, when Mr Winchester was murdered," the prosecutor Murugan Thangaraj SC said.

Australian Federal Police Assistant Commissioner Mr Winchester was shot dead in his car after he had pulled into his neighbour's driveway about 9.15pm on January 10, 1989, the trial heard.

Mr Winchester, Canberra's chief police officer, was killed with two bullets to the head, shot at close range.

Mr Eastman, 73, has pleaded not guilty to the murder.

The former treasury official, in dark pants, a red-checked shirt and a navy sweater, sat alone at a desk behind his lawyers throughout the day's hearing, a pen and notebook at the ready.

Mr Thangaraj painted a picture of a man who had resigned from the public service because of ill-health but became desperate to return.

At 41 years old, intelligent and physically fit, Mr Eastman felt he had been left on the "scrap heap".

Mr Thangaraj said Mr Eastman was not flush with cash, and the public service was not only where the man felt best-suited, but was a way out of the public housing flat he had found himself living in.

But as his battle to return the public service continued, Mr Eastman was accused of assaulting a neighbour.

Mr Thangaraj said Mr Eastman feared the consequences of a conviction for his return to the public service.

The Crown case against Mr Eastman is circumstantial, and prosecutors drew out the threads of evidence that would make up their case against him.

They pointed to a motive — in Mr Eastman's frustrating attempts to return to the public service and the assault of his the neighbour, Andrew Russo, and resulting charge of assault.

There were his efforts to buy a gun in the months before the alleged murder, and Mr Eastman's eventual purchase of what prosecutors say was the murder weapon - a Ruger 10/22 - from Louis Klarenbeek.

The murder weapon was never found.

Prosecutors also raised questions about Mr Eastman's unsatisfactory responses to police when asked where he was the night of the murder.

The police investigation was, Mr Thangaraj told the jury, unsurprisingly, the largest in Canberra's history and one of the biggest in the country.

Mr Thangaraj said the investigation followed hundreds of leads, and the Crown would address the other potential suspects in the killing that were eventually ruled out, including the Mafia.

The Mafia, he said, would not buy a weapon from a man who sold guns from a Queanbeyan backyard and advertised in The Canberra Times, nor would they walk down the street with it over their shoulder.

The court further heard the murder weapon had been fitted with a silencer, however, two shots had been heard on the night of Mr Winchester's alleged execution.

Mr Thangaraj said the killer had used supersonic ammunition, which created a sound as it broke the sound barrier, irrespective of whether a silencer had been fitted.

This was not the work of a professional, he said, as the shooter had used ammunition that defeated the purpose of the silencer.

Prosecutors will rely, too, on Mr Eastman's own mutterings to himself, captured by listening devices planted in his flat during the police investigation.

The trial also heard that in the months before Mr Winchester was killed, Mr Eastman allegedly told his solicitor he would kill the police officer and the ombudsman.

He wrote a letter to a confidant Irene Finke, telling her that he would probably kill someone to get attention paid to "the injustice that's been done to me", the court heard.

And Mr Thangaraj said that weeks before Mr Winchester's alleged murder, Mr Eastman met with the police chief and shadow attorney-general, wanting them to drop the assault charges against him.

It was his life, and a better living situation, that were at stake.

But the meeting did not go well for Mr Eastman, the prosecutor said; he felt he was"fobbed off".

He came to believe police were to blame for the charges, and that they had behaved corruptly.

"Mr Eastman had a new enemy, and his rage a new outlet," Mr Thangaraj said.

Mr Thangaraj said within weeks of that meeting, Mr Eastman "bought the murder weapon".

Mr Eastman wanted revenge, the prosecutor said, and he threatened to get back at police.

He wanted to murder Mr Winchester before the hearing for the assault on January 12, Mr Thangaraj said.

Mr Eastman told his general practitioner Dr Dennis Roantree that the police should be taught a lesson.

"The police were taught the harshest of lessons,” Mr Thangaraj told the jury, "and Mr Eastman made good on those threats."

The trial continues.