James Nesbitt portrays Colin Howell in a scene from The Secret.

So they killed them, framing the murders to look like a double suicide in a fume-filled car.

The lie lasted 18 years, and captivated the small, deeply religious Northern Irish town of Coleraine.

The shocking true story of sex, deceit and murder is the subject of the miniseries The Secret, now available on SBS By Demand streaming service.

WORST KEPT SECRET

Colin Howell seemed to be an upstanding citizen. He was a local dentist and sometime-preacher, and had four kids with his wife Lesley. But things weren’t as they seemed.

“Howell was addicted to pornography and abused patients, feeling them up while they were sedated,” investigative journalist and author Deric Henderson writes in his account of the murders, Let This Be Our Secret.

“He would go to London and stand outside massage parlours wanting to go in. He’d call up members of his church to say he had the urge again. The Baptists tried to wean him off porn. His life was a mess.”

He met Sunday school teacher Hazel Stewart at a Baptist church in 1990, and their intense affair began immediately.

When they were confronted by a pastor after being caught by a member of the congregation, the pair agreed to end it. But four months later, it was back on. Reports suggest the affair was the town’s worst kept secret. Howell and Buchanan would meet for sex wherever they could — Howell’s dental chair, Buchanan’s home when her husband, Trevor, a policeman, was away.

They wanted to be together, but the obvious solution of divorce was not allowed by the church. But there was one other option.

PERMISSION TO KILL

“Let this be our secret,” Howell wrote to his mistress about the idea to kill their spouses.

He had begun concocting his plan after a late night discussion with his wife Lesley. Her father had just died and she was emotional.

“This is going to be over soon. I am going to go to heaven. Maybe you and Hazel are meant to be together. I’ll never get over this. Trevor will never get over this,” she told her husband.

As Henderson writes in his book, Howell “felt in that moment that Lesley had actually given him permission to kill her: ‘It was a way out of this prison for her, the children and me’.”

Lesley Howell and Trevor Buchanan, real life victims of The Secret.Source:Supplied

As Lesley lay asleep on the couch in May 1991, Howell connected a hose to the exhaust pipe of his car and slipped the other end into Lesley’s mouth. As she woke in the process, Howell held his wife down until the job was done.

He stuffed her body in the boot of his car and drove to Buchanan’s house. She’d spiked her husband Trevor’s tuna sandwich with tranquillisers and his body lay on their bed, knocked out.

As Howell tried to use the same hose to gas Trevor with carbon monoxide fumes, he woke up. After a struggle, Howell eventually got the pipe down Trevor’s throat and killed him.

The hose was burnt, the sheets were cleaned, and Trevor’s body was stuffed in the boot with Lesley’s.

Howell drove the bodies 10km to the seaside suburb of Castlerock, where he arranged the scene to look like a suicide. He positioned both bodies in his Renault, placed family photos around them and turned up the volume of the church music playing on the tape player. He connected a hose to the exhaust and left the car running so fumes pumped in.

The scene was set, and it looked like a suicide.

James Nesbitt portrays Colin Howell in a scene from The Secret.Source:SBS

NO QUESTIONS ASKED

When police found the bodies, they declared it a double suicide. While people in the church community knew of the affair between Howell and Buchanan, it was concluded Lesley and Trevor must have ended their lives after finding out about their partners’ secret romance.

It was made even more convincing when Howell found a suicide note written by Lesley before her death and placed it around the house for police to find during the investigation.

Everything fell into place, and authorities didn’t ask too many questions. They declared the deaths a suicide pact.

Howell and Buchanan got what they wanted and they could start their life together out in the open. But it only last five years, with the pair breaking up in 1996 after Buchanan refused to marry Howell and move to Scotland.

HIS CONFESSION

Howell met Kyle Jorgensen in 1997 at bible study. A New Yorker, she had moved to Castlerock after a violent three year marriage to her first husband. Swept off her feet by Howell, they married after five months and Jorgensen fell pregnant with the first of five children they’d have together.

Howell was charming and conniving. Jorgensen was mesmerised by his biblical knowledge, but soon realised his twisted hypocrisy.

Over the kitchen table in 1998, while the kids were out playing, Howell told Jorgensen his big secret. And for a decade, he bullied and blackmailed her into keeping it a secret — even threatening to take his own life if she told anyone.

Jorgensen later told The Sunday Mirror she had tried to tell members of the church.

“I don’t want to hear it,” one church elder told her. “It’s before the cross ... you shouldn’t tell on other people before that time in their life.

“He abused patients, he is a compulsive liar, he was an adulterer in our marriage and murdered two people,” she added in the interview.

“Everyone thought he was this great Christian guy but they were so wrong. He was a monster.”

In 2009, 18 years after the murders, Howell cracked.

He was in debt, lost most of his money in a bad investment to recover Japanese gold in the Philippines and his son Matthew (from his marriage to Lesley) had died. Howell believed God was punishing him for his crimes.

Urged by church elders, he went to police and confessed to both murders as well as sexually assaulting female patients.

James Nesbitt as Howell and Genevieve O’Reilly as Buchanan in The Secret.Source:SBS

LOVERS TURN

By this point, Jorgensen had filed for divorce and moved back to the US with the kids. Buchanan had also moved on and remarried. But Howell wasn’t going down alone.

When Buchanan, who had remarried, was arrested following Howell’s confession, she maintained she was simply under Howell’s spell when the murders took place.

But during her trial, Howell eviscerated his former lover.

“Hazel and I were waltzing together all the time,” he said in court.

“All of the sidestepping was done together. I may have been the lead partner in the waltz but Hazel was dancing in co-operation with that dance.

“I wasn’t dragging her around the floor, making her put her foot to the left or the right. She was doing it in perfect harmony, on her own and willingly.”

While she refused to take the witness stand, interrogation tapes played in court showed Buchanan agreeing she had disposed of the hose, washed the sheets, and gave Howell her husband’s clothes to dress his dead body.

She was found guilty of murder by joint enterprise and sentenced to 18 years prison, while Howell was sentenced to life in prison with a minimum of 21 years.

At 57 years old, it’s reported Howell’s only regret about confessing is that Jorgensen didn’t stick by him after coming forward.

And it seems the manipulative and selfish former pastor is just as narcissistic as ever.

“At the moment he’s loving this whole TV thing,” one guard at Maghaberry Prison told Belfast Live. “He’s been a little edgy. He lets on to be modest but we know him, we know exactly what he’s like.”

The Secret is available to watch for free on SBS On Demand.