Colin Howell was sentenced to a minimum of 21 years in prison in 2010 after admitting murdering his ex-wife Lesley and also Trevor Buchanan - a policeman who was the husband of his mistress Hazel Stewart.
In 2011 Howell also pleaded guilty to sexually assaulting nine women patients in his dental surgery over several years.
Mr Howell met Hazel Stewart at a Bible study at their local baptist church and was also a licensed lay preacher.
He placed the bodies of Lesley and Trevor together in a car full of carbon monoxide which led police to believe the pair died in a suicide pact.
Actor James Nesbitt will play Mr Howell in the ITV drama The Secret, which starts this on Friday at 9pm.
Hazel Stewart, who was having an affair with Mr Howell at the time of the murders in 1991, was also found guilty of murder and sentenced to 18 years in prison.
Colin Howell eventually admitted his past crimes to second wife Kyle Jorgensen, who he also met at a church, in 1998.
She told the Sunday Mirror: "I really looked up to him as a teacher. His biblical knowledge was amazing.
"He knew it all, but the faith I believe he's been living is really very hypocritical.
"Everyone thought he was this great Christian guy but they were so wrong. He was a monster."