Vanessa Easton remembers Diane Stewart, her neighbor of many years, as a smiling, caring and outgoing school secretary.
“She was a lovely person anyone could strike up a conversation with,” says Vanessa, who has lived across the street from the Stewarts — Diane, her husband Ian and their two children — in Cambridgeshire, eastern England, since 1993.
They used to take care of each other’s cats when they went on vacation and enjoyed the neighborhood fireworks together.
“They seemed like a perfect, happy family,” Vanessa describes to the Stewarts. “It was so obvious how much they loved their children! Diane was full of love for them.”
But on June 25, 2010 everything changed.
Stewart said he returned home from shopping to find his 47-year-old wife, who had been doing laundry, lying on the floor. Shortly after, she was declared dead.
An investigation that same year concluded that the woman had suffered a sudden death from epilepsy (Sudep, for its acronym in English), which causes the death of about 600 people each year.
Although Diane had not suffered an epileptic seizure in 18 years, her death did not raise any suspicions.
But they did emerge with the death six years later of a second woman: Stewart’s fiancée, children’s author Helen Bailey.
Stewart had secretly drugged and suffocated Helen to inherit her fortune of more than $5 million, and dumped her body in a cesspool below her home in Royston, Hertfordshire, in southern England.
The suspicions
Convicted of Helen’s murder in 2017, police turned their attention to Diane’s death.
The investigation faced several major obstacles.
Not only was Diane’s body cremated, but complete toxicology tests were not performed during the 2010 post-mortem examination.
The only analysis was on an antiepileptic drug.
It was Stewart who authorized the cremation. During his testimony at trial, prosecutors accused him of doing it “so that there would be very little he could turn against him.”
However, the detectives followed a rather unusual path.
The brain as evidence
Diana had donated his brain to medical research, something Stewart consented to. Without that consent, this vital source of evidence would have been destroyed.
Superintendent Jerome Kent, of the Bedfordshire, Cambridgeshire and Hertfordshire Major Crimes Unit, says they discovered the brain was kept in hospital.
He explains that being able to access Diane’s brain was “absolutely crucial” and that without it “a conviction could not have been guaranteed.”
“It was also important to remember that if she had died of natural causes, we wanted to be able to tell the family that their concerns and suspicions were unfounded.”
According to neuropathologist Colin Smith of the University of Edinburgh, Scotland, the use of stored brain tissue as part of a police investigation is extremely unusual.
“I’ve never come across that situation before,” he tells the BBC.
But how did science help catch the killer?
Restricted breathing
A team of scientists and pathologists were recruited to re-examine Diane’s brain tissue.
Safa al Sarraj, a neuropathologist at King’s College Hospital in London, told the jury he found “changes in the brain consisting of early ischemia,” which he defined as “damage to cells due to lack of oxygen and blood supply.”
The scientist said that no trace of ischemia would be expected to be found in “a healthy breathing human being”.
It also revealed that it can be found when a person dies after suffering “restricted” breathing for “more than 30 minutes.”
Another expert witness, neuropathologist Kieren Allinson, found “no evidence of a recent seizure,” though he added that that didn’t mean it wasn’t a death from epilepsy.
Home Office pathologist Nat Cary, who gave evidence in 2017 at the Helen Bailey murder trial, said there was a possibility Diane’s breathing had been interfered with by the use of some kind of drug.
At the time of Diane’s death, Stewart called the emergency number.
“My wife had a seizure. She is in the garden », she told the operator. When asked if the woman was breathing, he replied, “No, I don’t think so, no.”
Their neighbor Victor Nickson helped guide air ambulance paramedics to the Stewarts’ home.
“I saw them put their thumbs down and shake their heads in response to the paramedics’ questions. CPR (cardiopulmonary resuscitation) stopped,” she said.
“One put his arms around Stewart, who was showing signs of stress and concern.”
Around this time, another neighbor, Vanessa, a nurse, came home and saw Diane’s body: “I remember thinking, ‘Thank God there’s no blood,'” she says.
It also notes that Diane’s death was “totally unexpected” and that although she suffered from epilepsy “she was well controlled.”
No real motive for Diane’s murder has yet become apparent.
Vanessa can’t find the answers.
“Ian had it all: a loving family, a wonderful life. His wife was a loving woman and a lovely person. Why did he throw it all away? Why did he do that? It’s something that doesn’t fit and I can’t understand », he says about Diane’s murder.
Vanessa’s husband, Paul, said of Stewart that he found it “pretty hard” to relate to him. “He would get very close when he spoke, invading your personal space,” he added, although “I never would have imagined that he would be able to kill someone.”
Six years later, Stewart would end the life of his new partner.
Helen’s murder
After Diane’s death, Stewart moved on with her life. He bought a sports car before beginning a relationship with Helen Bailey.
In April 2016, Stewart reported her missing.
Three months later, Helen’s body was found in a “smelly” cesspool next to the corpse of her dachshund, Boris.
Helen had written more than 20 books, including the popular Electra Brown series.
Her husband, John Sinfield, died in 2011 while on vacation in Barbados, drowning at sea after being swept away by the current.
She and Stewart met through a dueling website, bought a house together, and planned to marry.
Margaret Holson, who had become close to Helen in the months before her murder, says that what angers her most “is the thought that if more had been done to find out what happened to Diane, my friend Helen would still be here.”
“We didn’t have that information or evidence at the time,” Superintendent Kent replies.
“At the time of Diane’s death there was nothing to suggest that Ian Stewart had been responsible or that she had died at his hands,” it adds.
“He would have gotten away with the murder of Diane Stewart if it hadn’t been for the Helen Bailey investigation.
“I hope there aren’t too many more unidentified murders… but it is of course a possibility.”