The murderer of the children's author Helen Bailey was accused of killing his first wife after brain tissue posthumously donated to science showed signs of "prolonged restriction of breathing", a court has heard.

       Ian Stewart was found guilty of killing Ms Bailey, his fiance, in 2017, prompting police to re-investigate the sudden death of Diane Stewart seven years earlier.

       Ian Stewart, 61, went on trial at Huntingdon Crown Court on Tuesday accused of the murder of Ms Stewart, 47, which he denies.

       Stuart Trimmer QC, prosecuting, told jurors the defendant was "able to fool medical professionals by suggesting his wife, Diane Stewart, had died in the course of an epileptic fit" in 2010.

       Her death happened on the morning of June 25 at their family home in Bassingbourn, Cambridgeshire, while their children were out. Most of her remains were cremated, but the court heard that "she had donated her brain to medical research and brain tissue was kept".

       Stewart gave ‘differing accounts’

       Scientists and pathologists were instructed to re-examine the circumstances, and analysis of the brain tissue indicated that Ms Stewart's death was "most likely caused by a prolonged restriction to her breathing from an outside source", Mr Trimmer told the court.

       He said: "The conclusions, in short, are these: the cause of death was most likely caused by a prolonged restriction of her breathing from an outside source, and that the account given by Ian Stewart, the only other person on the premises, is directly contradicted by the medical evidence."

       The prosecutor said Stewart had given "differing accounts" of what happened, including that he had been out to Tesco and had come back to find his wife on the ground outside, and that she had been hanging out washing and he had found her lying next to the line.

       He answered "no comment" in police interviews, instead providing a prepared statement which said: "On that day I had left our home and, when I returned a short while later, I found Diane lying unconscious on the patio. I went inside to get the cordless house phone and dialled 999."

       Mr Trimmer said: "Diane Stewart's body was cremated, but her brain was kept for medical research and was, by a stroke of fortune, available for recent expert examination. Three pre-eminent experts have re-examined all the material and will be relied on by the Crown."

       He said Ms Stewart had a "mild form of epilepsy that was well controlled" and had not suffered a fit for 18 years. One consultant neurologist gave her risk of sudden unexpected death in epilepsy at the time as "extremely low – one in 100,000", he added.

       The prosecutor said the "narrative involving an epileptic fit that day appears to have originated from Ian Stewart rather than from any other source".

       Mr Trimmer said that, following Ms Stewart's death, Stewart's behaviour was "hard to square with the conduct of a grieving husband".

       "He was shortly out buying a sports car and embarked upon a new relationship," the barrister said. "Friends of Diane recall his behaviour at the funeral as being unusual."

       Stewart was flanked by four officers as he sat in the secure dock listening to the prosecutor open the case.

       The trial, set to last up to four weeks, continues.