Dr Iain West, a forensic pathologist based at Guy's Hospital, London, said injuries on the body of Carol Tucker could have been caused in a traffic accident.
Dr West was giving evidence on the 11th day of the trial of Mrs Tucker's husband, Nicholas, 46, an RAF Regiment Squadron Leader based at RAF Honington, Suffolk.
Mrs Tucker, 52, was found face down in a river at Lackford, Suffolk, on 21 July 1995. She died after the car being driven by her husband left the road.
Prosecutors allege that Sqn Ldr Tucker throttled his wife then staged the accident to cover his crime. He denies the allegation.
The prosecution has alleged that blood spots in Mrs Tucker's eyes were an indication that she could have been strangled before being placed in the water.
But Dr West disputed those claims. He told the jury at Norwich Crown Court that there was no evidence of throttling or strangulation.
He said there were no marks on Mrs Tucker's neck to indicate that she had been strangled.
Dr West said it was possible for a person to be strangled and for the killer to leave no marks on his victim's neck. But he said in those cases victims would not have any blood spots (petechial haemorrhaging) in their eyes either.
"I've never seen a case where there has been no marks on the skin, no bruising on the muscles, and yet, there have been these petechial haemorrhages," said Dr West. "I have never seen it."
He said an examination of Mrs Tucker's body revealed no clear cause of death. He said she could have drowned or she could have choked.
But he said there was no positive indication that she had been subjected to any assault.
"There are no marks that cannot be explained by a traffic accident combined with attempts to retrieve and resuscitate," said Dr West.
"There are no marks which say these are only marks which could have been caused during the course of an assault."
Prosecutors say Sqn Ldr Tucker killed his wife because he was infatuated with 21-year-old Dijana Dudukovic.
They say he met Miss Dudukovic while he was serving with the United Nations in the former Yugoslavia in the first half of 1995.
A Royal Marines officer who worked with Sqn Ldr Tucker in the former Yugoslavia told the court earlier that Sqn Ldr Tucker's relationship with Miss Dudukovic undermined the effectiveness of his team of observers.
But yesterday other servicemen who worked with the RAF officer in the former Yugoslavia described him as professional, hardworking and meticulous.
Captain Ralf Tieken, an officer in the Dutch Army said: "I thought he was a professional and hardworking soldier. And I regarded his team as one of the most efficient teams."
The hearing continues today.