A pathologist tasked with reviewing the original report of Susan Burdett's post-mortem examination agrees her injuries were akin to a car crash and were "rapidly fatal".

Burdett suffered "at least five separate blows to the head", Dr Simon Stables said today.

The doctor's answer came as he is giving evidence on day five of Malcolm Rewa's retrial for the murder of the 39-year-old accounts clerk in her Auckland home in 1992.

Rewa, a 65-year-old serial rapist, was convicted of Susan Burdett's rape in 1998 but two juries that year were unable to decide whether he was also responsible for her death.

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Earlier today a member of the public sitting in the gallery sent a verbal barb in Rewa's direction as the man left courtroom.

"I hope you rot in jail," the man said.

Rewa, with his head bowed in the dock, did not react to the comment.

When Burdett's body was found by a friend on Wednesday, March 25, 1992, it quickly became apparent she had been bludgeoned to death.

A baseball bat, which Burdett kept as protection, was found lying next to her body on her blood-soaked bed.

"You can't get the exact weapon, all you can give is an opinion," Stables said.

But he added: "It would be consistent with a baseball bat being used, these injuries would be consistent with that."

Susan Burdett was killed in her Auckland home in 1992. Photo / File
Susan Burdett was killed in her Auckland home in 1992. Photo / File

However, earlier in the trial forensic scientist Dr SallyAnn Harbison said she could only detect "four tiny spots of blood" on the bat with the help of a microscope.

A test to establish if the blood was human came back inconclusive and Harbison said there was no forensic evidence which could directly link the bat to Burdett's killing.

Burdett, who weighed 62kg and stood 168cm tall, also showed "absolutely classic" signs of defence injuries to her hands as Stables surmised "she has tried to protect herself" from her attacker.

Dr Timothy Koelmeyer, who carried out the original examination, said Burdett's injuries were "rapidly fatal", a phrase Stables agreed with.

But trying to determine time of death, Stables said, was impossible to do with any degree of accuracy.

"Trying to determine time of death is really the last bastion of forensic pathology," he said.

The baseball bat the Crown alleges was used to kill Susan Burdett. Photo / Sam Hurley
The baseball bat the Crown alleges was used to kill Susan Burdett. Photo / Sam Hurley

The doctor said the wounds Burdett suffered also required "a significant amount of force".

"To fracture through the base of the skull requires a significant amount of force ... it is something that is usually seen in car accidents and you can imagine the force in that," he said.

He explained the human skull was thicker around the base.

Crown prosecutor Gareth Kayes alleges Rewa was Burdett's attacker.

He said earlier in the trial that Rewa entered Burdett's home on March 23, 1992, and raped and murdered her.

Rewa's lawyer Paul Chambers, however, has accused Burdett's son Dallas McKay of killing his mum.

McKay was once treated as a suspect by police during the investigation into Burdett's death.

He strenuously denied killing his mum.

Malcolm Rewa is on trial and accused of murdering Susan Burdett for a third time. Photo / Michael Craig
Malcolm Rewa is on trial and accused of murdering Susan Burdett for a third time. Photo / Michael Craig

The jury has also been shown a graphic and somewhat eerie silent police video of the crime scene, which had been filmed at the time.

Rewa has been convicted of raping several women between 1987 and 1996.

Burdett's killing, Kayes alleged, displayed a "striking resemblance" to Rewa's other sexual assaults.

Teina Pora was twice wrongly convicted for murdering Burdett on the back of a false confession.

He was arrested when just a 17-year-old and spent 22 years in prison before the Privy Council quashed his conviction in 2015.

He has since received an apology from the Government and $3.5 million in compensation.

A stay of proceedings for a murder prosecution against Rewa was applied by the Solicitor-General in 1998, but two years ago the Deputy Solicitor-General reversed the stay thus allowing the current trial.

A stay had never before been lifted in New Zealand's legal history.

The trial continues.

Malcolm Rewa being escorted to the Otahuhu police station by detectives in May 1996. Photo / NZ Herald
Malcolm Rewa being escorted to the Otahuhu police station by detectives in May 1996. Photo / NZ Herald