The driveway where Mr Winchester sat slumped in the driver's seat of the Ford sedan formed the crime scene in what would become the biggest police investigation in Canberra's history, an investigation that led to the charging of public servant David Harold Eastman for murder.

Mr Winchester, the assistant commissioner of police, was shot in the head on January 10, 1989.

The 72-year-old Mr Eastman, on trial in the ACT Supreme Court, has pleaded not guilty.

Forensics officer Murray Duffus was one of the first officers called to the crime scene. He agreed under questioning by defence barrister George Georgiou SC that the senior officers were trampling on the crime scene, but they had told him to "f--k off" when he asked them to move away.

He told the court that police tried to limit interactions with crime scenes as much as possible to avoid contamination, or evidence such as fingerprints removed, obscured or added.

He admitted that with the senior officers present he had little control over the scene, and the court heard it wasn't until the acting superintendent of the forensic services division arrived that the area was secured.

That officer, Peter Nelipa, told the court he had relayed instructions to officers at the site that no one was to enter the area until he had cleared it.

But when he arrived about 9.50pm he found numerous police officers in the street and two senior police officers on the grassed strip near driver's side door. There was an ambulance parked on the driveway, and a number of police cars parked in the street.

He said he was concerned at the number of people present.

"Ideally, no one should be there at all," he told the court.

"My plans for examining the scene went out the window."

He said his first thought was to gain control of the scene, a process that took more than an hour.

He ordered a systemic search of the street, and then directed all cars away from the scene.

He began a detailed examination of the crime scene about 11.40pm that night.

He vaccumed the driveway, to preserve any trace elements that might prove useful in the police investigation.

The jury on Monday saw the confronting photographs Mr Nelipa had captured of the scene.

Mr Winchester was slumped in the front driver's seat with one foot out of the car, and the officer told the court he had concluded that the man had been shot while getting out of the car.

The officer also recorded a bullet wound in Mr Winchester's right temple, and another in the back of the head, and concluded it was the latter that had been inflicted first.

There was a blood-soaked box of ammunition on the front passenger seat, and splashes of blood on the inside roof of the car and the inside driver's side rear window.

Later, when searching the grass strip near the driveway, Mr Nelipa said found two spent cartridges.

There was no firearm at the scene. The court has heard that the murder weapon was never found.

The trial continues.

Correction: An earlier version of this article incorrectly stated Mr Nelipa's last name.