There is a chance that Thursday night could be his last night in prison after more than 19 years behind bars for killing Assistant Federal Police Commissioner Colin Winchester near the ACT police chief's Deakin home in 1989.

Mr Winchester was assassinated as he began to get out of his car in his neighbour's driveway.

It was a crime that shocked the nation and became one of the most notorious police killings in Australia's history.

Eastman was convicted of the murder after a lengthy trial in 1995, but an inquiry recommended earlier this year that the conviction be quashed, after serious flaws were identified with the forensics linking him to the scene.

The ACT Supreme Court is now considering Eastman's fate, and he could potentially walk from the Alexander Maconochie Centre on Friday, should it decide to quash his conviction without ordering a retrial.

His former lawyer and campaigner Terry O'Donnell said on Wednesday that Eastman was now just waiting in suspense for his day of judgment. Mr O'Donnell said he had spoken with Eastman recently.

"As far as I'm aware he's coping very well and he's just looking forward to dealing with it as it comes," he said.

The full bench of the ACT Supreme Court will decide whether to quash Eastman's conviction, quash it and order a retrial, maintain the conviction, or recommend a pardon.

Should the court order a retrial, the buck will be passed to the Director of Public Prosecutions, who would decide whether to try Eastman again.

"Irrespective of what they do, he can't get a fair retrial," Mr O'Donnell said.

ACT correctional authorities have also offered Eastman, as with all prisoners, support and preparation before his possible release.

A Justice and Community Safety Directorate spokeswoman said all prisoners are given pre-release planning for matters such as accommodation, identity documents, bank accounts, health and rehabilitation programs, and employment or welfare, if needed.

They are also offered support through the Throughcare extension program to help them transition back into the community.

"If released, ACT Corrective Services will provide Mr Eastman with the same support as other detainees who are released from the AMC," the spokeswoman said.

Long-term detainees can often struggle to adjust to life outside, the spokeswoman said.

"Living in the community is quite different to the regimented nature of prison life and society, technology and other things may have changed significantly since that person was imprisoned," she said.

The full bench will deliver its judgment at 2.15pm on Friday.