Ian Stewart was found guilty of drugging and killing the children's author following a long-planned plot to acquire her riches on Wednesday after a six-week trial at St Albans Crown Court.
Driven by greed, the 56-year-old man drugged and suffocated his fiancé before dragging her lifeless body into a cesspit hidden deep below their luxury Hertfordshire home, where her body lay undiscovered for three months.
Stewart befriended vulnerable widow Ms Bailey on the internet in 2011 – earning his way into her trust and later her £3.3 million estate after launching a "love-bombing" offensive.
The murder plot was uncovered as a police investigation was launched after the computer software expert told detectives the Electra Brown writer had disappeared after leaving a note saying she needed time to herself.
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Ian Stewart was found guilty of drugging and killing Helen Bailey
However, the scam was foiled when it emerged he stood to gain from Ms Bailey’s death and he had moved her money into an account the couple shared the same day she was killed.
The police swooped in and a search of the £1.5million home resulted in the discovery of the 51-year-old's body, along with her dog Boris, in a tank of human sewage underneath the couple's garage on July 15 last year.
Stewart arrest was caught by a body camera worn by one of the officers, and shows the murderer being worried about the open door to the garage, where his victim's body was later found.
The clip starts by showing police officers going to the home in Royston, where Jamie, Stewart’s son opened the door.
Shortly afterward the 56-year-old man can be seen coming downstairs in his dressing gown after being woken up by Jamie.
Stewart will be sentenced on Thursday
Bloody hell, why?
And as he was told be was being arrested for murder, Stewart appeared shocked as he said: “You’re kidding.”
The calculated man then sat down on the staircase before he said: “Bloody hell, why?” and “What happened?”.
Stewart also said “the garage door is open,” as he was taken upstairs to get dressed, a key piece of evidence later used in court.
Stewart of Baldock Road, Royston, Hertfordshire was found guilty of murder, fraud, three counts of perverting the course of justice and preventing a lawful burial and will be sentenced on Thursday.
The author's shattered family welcomed the verdict, but said her death had left them lingering in a "long shadow of loss".
Ms Bailey's body, along with her dog Boris, was found in a tank of human sewage
Miss Bailey's brother, John, sat in court for almost every day of her killer's trial, while their elderly mother Eileen broke down as she gave her testimony.
The family said in a statement: "Despite this victory for justice there can be no celebration.
"Our families have been devastated and nothing can ever bring Helen back to us, or truly right this wrong.
"A long shadow of loss has been cast over the lives of so many who will always remember Helen with enduring love and affection."
Detective Chief Inspector Jerome Kent said: "To kill somebody was despicable enough, but to dispose of her in the way he did and lie to everyone including his own children shows how wicked and despicable that man is."