The murder trial of David Harold Eastman is expected to start next week.
Mr Eastman was arraigned before nearly 500 potential jurors at Albert Hall on Monday morning.
Mr Eastman is accused of the 1989 assassination of Assistant Federal Police Commissioner Colin Winchester.
Mr Winchester was gunned down while sitting in his car in the driveway of his neighbour's Deakin home on the night of January 10, about 9.15pm.
Mr Eastman, now in his 70s, has pleaded not guilty.
The trial is estimated to last about six months.
The empanelment was held at Albert Hall as the courtroom's at the ACT courts complex were too small to hold the large number of people.
The Sheriff's office usually issues about 100 jury notices for a trial in the ACT Supreme Court.
Potential jurors began lining at Albert Hall from 7.20am on Monday morning and were ushered inside from about 8am.
Mr Eastman and his legal team arrived shortly before 10am and entered the building via a rear entrance.
The prosecution team and judge arrived about 9.30am.
The court was closed for the arraignment.
It is understood more than 100 potential jurors will return tomorrow to continue empanelling.
The empanelment process will be completed this week, with opening addresses by the prosecution and defence after June 12.