In 2009, dentist Colin Howell's then wife Kyle forced him to confess to police that he had murdered his first wife along with the husband of Hazel Stewart, setting off a chain of events that shocked Ireland and Britain.
Howell had killed his wife Lesley and later Trevor Buchanan at their Co Derry homes in May 1991, when he attached part of a baby's feeding bottle to a garden hose, gassing them with carbon monoxide as they slept.
Kyle, who returned to her native America after her husband's confession, had known for a decade that the man she was married to had killed Mrs Stewart's then husband Trevor (32) and his first wife Lesley Howell (31).
She later told a tabloid newspaper that he blackmailed and coerced her into keeping his secret.
"Everyone thought he was this great Christian guy but they were so wrong. He was a monster."
A leading member of the evangelical church, Howell was addicted to online pornography, a serial adulterer and was abusing female patients under heavy sedation at his Ballymoney clinic.
In the run up to his confession he was faced with a mounting unpaid tax bill and had sold his share in two dental practices to invest in a doomed mission to find gold, supposedly buried in caves in the Philippines by Japanese troops in the 1940s. The gold deal was a scam and he lost everything.
It was this financial ruin along with the death of his eldest son Matthew, while on university placement in St Petersburg, that are thought to have prompted Howell to reveal the deadly secret.
Matthew was the last word his wife called out before he forced a hose to her face that was attached to the exhaust of their car, holding a duvet over her head until she stopped breathing.
He then dressed her and carried her to the boot of the car, placing a blanket over her head and a bicycle on top of her body, driving from his Knocklayde Park home in Coleraine to the Buchanans' Charnwood Park house where Trevor was asleep in his marital bed.
From the garage he repeated his garden hose trick, placing it close to Mr Buchanan. However, the RUC scenes-of-crime officer woke up and a struggle ensued.
Howell pinned him down and with the RUC man now dead he carried him to the car boot placing him beside Mrs Howell's body.
Hazel Stewart, a court was later told, disposed of the hosepipe and cleaned the room where her husband died, which was the main joint enterprise element of her conviction.
Howell drove to a row of houses at Cliff Terrace, Castlerock, known as the Twelve Apostles.
One had been owned by Lesley's father, Harry Clarke, who had collapsed and died at his daughter's home 12 days earlier.
In its garage, he pulled on a pair of plastic surgical gloves and placed Mr Buchanan in the driver's seat and Mrs Howell in the boot with family photographs beside her.
Howell connected a length of vacuum hose to the exhaust, with the other end in the boot, switching on the ignition before cycling home.
It was considered the 'perfect crime' and no one questioned the rather bizarre explanation for the deaths of the two love rivals, until Howell eventually confessed.
He pleaded guilty to the murders in 2010 and is serving a minimum of 21 years in prison.
He later turned State witness to give evidence against his former partner who denied responsibility for the double murder.
The jurors in Stewart's 15-day trial unanimously accepted that she knew about the plan in advance and, in the case of her husband, actively facilitated it by ensuring he was drugged and allowing Howell into her home.
A former Sunday school teacher, she was found guilty and jailed for a minimum of 18 years in 2011.
Her appeal in 2013 against the conviction for the murder of Mrs Howell was dismissed.
She had had dropped the appeal for the murder of her husband on advice of previous counsel that it was groundless.
In 2018 detectives took the former dentist from Maghaberry prison to be interviewed about the alleged sexual assaults carried out against Hazel Stewart.
Stewart had previously been questioned by specialist officers about the incidents that were said to have happened while she was sedated by Howell.
The case is now in the later stages of consideration by the Public Prosecution Service with a decision on whether he will face charges connected to the woman, tried as his accomplice, but who now may be called to give evidence as his alleged victim.
