Overview of Casefile Presents: Case 356 — Leslie Howell & Trevor Buchanan
This episode examines the 1991 deaths of Leslie Howell and Trevor Buchanan in Coleraine, Northern Ireland—initially treated as a tragic suicide pact, but later revealed to be a carefully staged double murder. The case centers on Leslie’s husband, dentist Colin Howell, and Trevor’s wife, Hazel Buchanan, whose affair with Colin set off a chain of deception, religious hypocrisy, emotional abuse, and eventual murder. For nearly 20 years, the deaths were accepted as suicides before Colin’s confession exposed the truth.
What Happened
The apparent suicide pact
- Leslie Howell and Trevor Buchanan were found dead in a garage in Castle Rock from carbon monoxide poisoning.
- At the scene:
- Trevor was slumped in the driver’s seat of a Renault.
- Leslie was found in the back of the car with personal items around her.
- A hose had been attached to the exhaust to feed fumes into the vehicle.
- Police and the coroner initially concluded the deaths were the result of a suicide pact driven by guilt, shame, depression, and marital breakdown.
The backstory
- Leslie and Colin Howell were devout Baptists with four children.
- Their marriage deteriorated over time due to:
- Colin’s controlling, misogynistic attitudes
- Financial stress
- Leslie’s isolation as a stay-at-home mother
- Leslie’s depression and grief after the deaths of both parents
- Colin later began an affair with Hazel Buchanan, Trevor’s wife.
- Leslie and Trevor eventually discovered the affair and were subjected to church discipline and counseling.
The Murders and Staging
Colin Howell’s confession
Years later, Colin confessed that:
- He decided to kill Leslie and Trevor after convincing himself it was a “merciful” solution.
- He planned to make the deaths look like suicide.
- He used sedatives and carbon monoxide to carry out the killings.
- Hazel was not merely a bystander—he said she knew about and assisted in the plan.
The staged scene
According to Colin’s confession:
- Leslie was killed first at the Howell home.
- Her body was transported to the Buchanans’ home.
- Trevor was then killed in the same way.
- The Renault was driven to Castle Rock and positioned to look like the couple had died together in a suicide pact.
- Leslie’s old crumpled note was used to bolster the suicide theory.
Why the Case Was Missed
Major investigative failures
An ombudsman later found the original investigation deeply flawed:
- Police became fixed on the suicide-pact theory early.
- Key forensic work was not done.
- Important evidence was not properly collected or examined.
- Suspicious details were overlooked, including:
- Trevor’s leg trapped in the car door
- The open driver’s window
- Colin’s bump on the head
- Inconsistencies in Colin and Hazel’s accounts
Why suspicion eventually grew
Detective David Green later voiced concerns that:
- Leslie’s “suicide note” may have been written much earlier.
- Colin may have been drugging Leslie before her death.
- Leslie’s father, Harry, may also have been poisoned to secure an inheritance.
- Trevor did not seem suicidal and had made future plans.
Court Outcome
Colin Howell
- In 2009, Colin confessed to church elders, then to police.
- He pleaded guilty to the murders.
- In 2010, he was sentenced to life imprisonment with a minimum term of 21 years.
Hazel Buchanan
- Hazel denied murder but was later convicted as an active participant in the killings.
- The court found she had helped plan, facilitate, and cover up the murders.
- She received a life sentence with a minimum term of 18 years.
- A 2025 appeal to reduce her sentence failed.
Other Crimes and Later Developments
Sexual assault allegations
Police later investigated reports that Colin had sexually assaulted sedated female patients at his dental clinic.
- Several women described inappropriate touching while under sedation.
- Colin admitted the assaults.
- He received an additional prison sentence and was placed on the sex offenders register.
Possible death of Leslie’s father
- Investigators also revisited the death of Leslie’s father, Harry.
- No definitive evidence linked Colin to his death, though suspicion remained.
Key Takeaways
- The case is a stark example of how faith, secrecy, shame, and manipulation can distort truth.
- Colin Howell presented himself as a devout Christian and respectable family man while committing horrific crimes.
- Hazel Buchanan’s role remained controversial, but the court ultimately found her culpable.
- The original police investigation failed to properly challenge the suicide narrative, delaying justice for decades.
- Leslie and Trevor’s families were left to live with the false public story that they had died by suicide.
Lasting Impact
- The victims’ children continue to defend their parents’ memory.
- Leslie’s children reject the idea that Hazel should be seen primarily as a victim.
- Trevor’s family has had to endure years of stigma caused by the false suicide narrative.
- The case remains one of the most disturbing examples of a murder staged as a suicide pact in recent Irish true crime history.