Colin Howell was born on March 14, 1959, in Portadown, Northern Ireland. He trained as a dentist and became a devout Baptist lay preacher. In July 1983, he married Lesley Clarke, a nurse, and together they had four children. Later, he had an affair with Hazel Elkin, married at the time to RUC officer Trevor Buchanan. Howell’s wealth and religious standing masked a complex private life. After the murders, he remarried — to Kyle Jorgensen from New York — and fathered five more children.

In May 1991, Howell and Hazel plotted the murders to appear as a suicide pact between Lesley and Trevor. On May 19, 1991, the bodies of Trevor Buchanan (aged 32) and Lesley Howell (31) were found in a car, inside Lesley’s father's garage in Castlerock, filled with exhaust fumes. The RUC ruled it a suicide pact and the investigation ended — even though suspicious details (e.g., open window, Buchanan’s leg hanging out) were noted.

In 2009, guilt and financial ruin led Howell to confess to church elders. He handed himself in to police on January 29, 2009, admitting he staged the murder pact with Hazel . On November 18, 2010, he pleaded guilty to both murders and, on December 3, 2010, was sentenced to life with a minimum of 21 years.

Howell's accomplice, Hazel Stewart, maintained she was coerced but was convicted on March 2, 2011, and sentenced on March 16, 2011, to life with a minimum 18-year term. Police later admitted flaws in the original investigation, and the case was heavily criticized in 2011.

On May 17, 2011, Howell pleaded guilty to the sexual assault of nine female patients over several years, resulting in the loss of his NHS pension.