David Eastman has begun his bid to head off a new trial over the killing of top AFP officer Colin Winchester.

Assistant Commissioner Winchester was shot in his car after arriving home in January 1989.

Mr Eastman spent 19 years in jail after being convicted of the killing.

But he was released in 2014 after an inquiry found there had been a miscarriage of justice, and a retrial was ordered.

Mr Eastman is seeking a permanent stay on the charge.

His lawyers said they would argue against a new trial on several grounds, including that the crown case was weak.

However his barrister, Mark Griffin, told the court there was no single issue that would secure the stay.

"We are asserting there is no one silver bullet," he said.

"It's a collection of circumstances."

Important issues not disclosed during trial: Lawyers

Mr Eastman's lawyers opened their arguments with claims the prosecution at the original trial did not disclose important issues to the defence.

They questioned a key member of the prosecution team, John Ibbotson, over the management of forensic evidence.

It was the flaws in the forensic case which led to the 2014 finding that there had been a miscarriage of justice.

However the inquiry found the prosecutors operated with integrity and that any omissions were inadvertent.

Mr Ibbotson told the court he thought everything necessary had been passed on to the defence.

"Whatever needed to be disclosed was disclosed," he said.

Mr Eastman's team also argued the circumstantial case against him is weak, despite claims to the contrary by the DPP.

Other issues to be raised over the course of the application are the long delay, Mr Eastman's personal circumstances, and the risk that the case's long-running publicity could jeopardise a trial.

Acting Justice David Ashley told the court the stay application was unusual.

"It's something of a hybrid between a trial and an appellant proceeding," he said.

The hearing is expected to run for around two weeks, with several witnesses to be called.

But any outcome is likely to be delayed, while the ACT's Court of Appeal considers some outstanding issues about admissible evidence.

The hearing has already been delayed - first when Mr Eastman's lawyer became ill and withdrew, and later when the original judge appointed stood down after a successful challenge, over an apprehension of possible bias.