The star witness for the case against Gordon Wood acted like a prosecutor and not an impartial expert witness after investigating police "poisoned his mind", a court has heard.
Mr Wood was found guilty in 2008 of the murder of his model girlfriend Caroline Byrne. He spent three years in jail before he was sensationally acquitted by the Court of Criminal Appeal in 2012.
Associate Professor Rod Cross gave evidence at Mr Wood's trial that Ms Byrne could not have committed suicide at The Gap, in Watsons Bay, in June 1995.
Associate Professor Cross told the jury that, given the short run-up distance available, she could not have propelled herself as far from the cliff as she landed and must have been thrown.
Mr Wood, 54, is now suing the state of NSW for millions of dollars in damages, claiming malicious prosecution.
In a hearing in the NSW Supreme Court on Wednesday, Mr Wood's barrister Bruce McClintock, SC, said Associate Professor Cross, a retired University of Sydney physicist, was extensively involved in the police investigation for years.
It was his expert evidence that convinced the police and the Office of the Director of Public Prosecutions to prosecute Mr Wood for murder.
However, at trial, he gave evidence as an impartial expert witness.
Mr McClintock said: "We say that Professor Cross himself was a prosecutor and he was malicious and the state is liable for that malice."
Alternatively, the use of Associate Professor Cross is evidence of malice by the police and the prosecution, he said.
Mr McClintock said lead investigator Detective Inspector Paul Jacob "poisoned" Associate Professor Cross' mind by recounting a false story about Mr Wood asking to see Ms Byrne's breasts at the morgue.
The story originated from Ms Byrne's former boyfriend, then-police officer, Andrew Blanchette, and was "false".
Detective Inspector Jacob also told Associate Professor Cross that a witness, Irish artist John Doherty, had seen a young woman and two men arguing at The Gap in the hours before Ms Byrne died.
"It's obvious that the police - whether intentionally or not - poisoned Professor Cross' mind by putting these things into it," Mr McClintock said.
"One wonders why Detective Inspector Jacob thought it was appropriate ... unless he wished to corrupt his perception of what was going on."
After the trial, Associate Professor Cross published a book called Evidence for Murder: How Physics Convicted a Killer, which the Court of Criminal Appeal said further demonstrated bias and opinions about biomechanics that strayed from his field.
Mr McClintock said Associate Professor Cross and detectives repeatedly changed their theory as to what happened to Ms Byrne to fit their case against Mr Wood.
In acquitting Mr Wood, the appeal judges were unanimous in finding that there was insufficient evidence to prove beyond a reasonable doubt that Mr Wood had killed Ms Byrne.
They found that it was unclear how Ms Byrne fell to her death or whether Mr Wood had any involvement.
The hearing continues before Justice Elizabeth Fullerton.
