The possibility that a sex act gone wrong could have led to An An Liu being strangled to death was raised yesterday at the High Court murder trial of her husband, Nai Yin Xue.

Xue's lawyer Chris Comeskey asked the pathologist who performed the autopsy on Ms Liu, Dr Timothy Koelmeyer, about auto-erotic asphyxiation - reducing oxygen to the brain with the aim of achieving heightened sexual pleasure.

The doctor said cases occurred in Auckland from time to time and he was aware it could result in accidental death. It was rarely seen in criminal cases and usually involved complicated bindings, he added.

Mr Comeskey asked him if he could rule out accidental asphyxiation as a cause of Ms Liu's death, "given the signs are there".

"If I was really pushed into a corner, I would say I can't rule out an accident, but I don't favour it," he said.

After questions from prosecutor Aaron Perkins and trial judge Justice Hugh Williams, he said pressure would need to be applied after someone became unconscious for them to die.

The pressure would have to come from a hook on a wall - or by someone pulling on the tie. It was likely Ms Liu would have lost consciousness within 45 seconds but could have taken up to three minutes to die.

Ms Liu was found dead in the boot of Xue's car with a yellow, black and silver tie knotted around her neck and partly covering her eyes. She was naked apart from a pair of white gloves.

The Crown alleges Xue killed her and dumped her body in the boot of his car before fleeing to Melbourne, where he abandoned the couple's 3-year-old daughter and then went to the United States.

Asked by Mr Comeskey for an explanation for Ms Liu's blood being found underneath her fingernails, Dr Koelmeyer said he could not offer one.

He also could not say when she was killed, confirming it could have happened up to seven days before the post mortem on September 20, 2007.

Police believe she was killed on the evening of September 11. Dr Koelmeyer said he told police to "make very sure it was the 11th" but, under cross-examination, he could not rule out that she died later.

Earlier, he told the court Ms Liu was killed from ligature pressure rather than manual strangulation.

The tie around her neck was the most likely cause but he could not rule out a pendant she wore around her neck having some effect.

He said he had never seen a strangulation where the eyes were covered and suggested the tie could have slipped because it was quite loose. "I think we have to be careful [about whether] it was an intended blindfold."

When he examined the body he was surprised she was not as badly decomposed as he would have expected. Mr Comeskey asked whether lying in the boot of the car, with the air contained, could have been a factor.

He said it could have been and had suggested to police they should investigate the possibility, although he was unsure if tests were carried out.

The prosecution is expected to close its case against Xue today.