Hazel Stewart: The Carbon Monoxide Killer Who Staged Gas Suicides with Her Lover

In the quiet suburbs of Coleraine, Northern Ireland, two families were shattered by what appeared to be tragic accidents. In 1991, Lesley Howell was found dead in her bed, the victim of a supposed carbon monoxide leak from a faulty gas heater. Just over a year later, in 1992, Trevor Buchanan met the same fate in his home, his death ruled a suicide by the same insidious method. For nearly two decades, these cases lingered as heartbreaking mysteries, until a shocking confession revealed a darker truth: both deaths were meticulously staged murders orchestrated by lovers Hazel Stewart and Colin Howell, who conspired to eliminate their spouses and build a new life together.

Hazel Stewart, a churchgoing mother and nurse, and Colin Howell, a respected dentist, seemed like pillars of their community. Their affair ignited a ruthless plan fueled by passion and desperation. What followed was a chilling tale of deception, where everyday household appliances became instruments of death. This story examines the facts of their crimes, the long-buried evidence, and the justice that finally prevailed, always with profound respect for the innocent lives lost—Lesley, a devoted mother of four; Trevor, a caring father and firefighter; and the children left in unimaginable grief.

At its core, the Hazel Stewart case exposes the banality of evil in domestic settings. The couple’s method—exploiting carbon monoxide poisoning to mimic accidents or suicides—highlighted vulnerabilities in forensic practices of the era. Their story serves as a stark reminder of how love twisted into obsession can lead to unimaginable horror, prompting reforms in death investigations worldwide.

Background: Lives Intertwined in Coleraine

Coleraine, a coastal town in County Londonderry, was home to two unassuming families in the late 1980s. Hazel Thompson, born in 1964, grew up in a strict Protestant household. She trained as a nurse and married Trevor Buchanan in 1987. Trevor, a popular firefighter and former policeman, was known for his warmth and dedication to his two young sons, Andrew and David. Their marriage appeared stable, though Hazel later claimed it had grown strained.

Across town, Colin Howell, born in 1959, was a successful dentist married to Lesley Eakin since 1984. The couple had four children and were active in the local Baptist church, where Colin led youth groups. Howell projected an image of piety, but beneath it lay a controlling personality prone to manipulation. He and Hazel first crossed paths at a church event in 1988, sparking an immediate attraction. What began as flirtation escalated into a full affair by 1989, setting the stage for tragedy.

The lovers met secretly in motels and cars, their passion clashing with their commitments. By 1990, both expressed frustration with their marriages. Howell, in particular, began fantasizing about a future together, confiding in Hazel his willingness to “remove obstacles.” Hazel, though hesitant at first, became complicit, drawn into a web of shared secrets and illicit thrill.

The First Crime: Colin Howell’s Murder of Lesley

On the night of May 20, 1991, Colin Howell executed his plan. He had modified the gas heater in the family home’s attic room, blocking its flue to produce lethal carbon monoxide. That evening, after putting their children to bed, Howell led Lesley to the attic under the pretense of intimacy. There, he sedated her with a mixture of drugs, including Co-dydramol painkillers and Temazepam, before positioning her unconscious body near the faulty heater.

Lesley, 31, died painlessly in her sleep from carbon monoxide poisoning, her blood saturated with the gas. Howell arranged the scene to suggest an accidental leak or suicide, even leaving a suicide note forged in her handwriting. The next morning, he “discovered” her body and called emergency services, feigning devastation. Post-mortem examinations confirmed carbon monoxide as the cause, with no suspicion of foul play. Police ruled it a tragic accident, exacerbated by the heater’s poor maintenance.

Howell wasted no time. Within weeks, he sold the family home and began openly dating Hazel, announcing their engagement. The community mourned Lesley while praising Howell’s resilience, unaware of the calculated precision behind the facade.

Hazel’s Knowledge and Accomplice Role

Hazel Stewart was deeply involved from the outset. She helped Howell dispose of drug evidence and provided an alibi during the critical hours. In taped confessions years later, Howell revealed that Hazel not only knew the plan but encouraged its execution, viewing it as the path to their happiness. Their affair intensified post-murder, with Hazel attending Lesley’s funeral while secretly reveling in the outcome.

The Second Murder: Trevor Buchanan’s Death

Emboldened by success, the couple turned to Hazel’s husband. Trevor, 32, lived with Hazel and their boys in a modest home. Suspicious of her infidelity after Howell’s wife died, Trevor confronted her, but Hazel deflected with lies. On January 8, 1992, she drugged Trevor’s hot chocolate with sleeping pills and alcohol, rendering him unconscious.

With Howell’s guidance, Hazel replicated the method: she blocked the flue on their kitchen heater, dragged Trevor’s limp body into the living room, and arranged pillows to contain the gas. Carbon monoxide filled the room overnight. The next morning, Hazel “discovered” him, performing CPR for show before paramedics arrived. Like Lesley’s case, toxicology showed high carboxyhemoglobin levels, and the coroner ruled suicide, citing Trevor’s supposed depression amid marital woes.

Trevor’s family questioned the verdict— he was upbeat and planning a family holiday—but lacked evidence. Hazel collected insurance payouts totaling over £100,000 and moved in with Howell, marrying him in 1997 and having two more children. Their union lasted 12 years, a veneer of normalcy masking guilt.

The Elaborate Cover-Up and Community Deception

Howell and Stewart’s success hinged on exploiting 1990s forensic limitations. Carbon monoxide leaves minimal traces, often mimicking natural deaths. They coached each other on alibis, destroyed incriminating notes, and immersed themselves in church activities to bolster credibility. Howell even lectured on Christian forgiveness, drawing grieving families into his orbit.

The couple’s children suffered silently. Lesley’s sons grew up idolizing Howell, while Trevor’s boys grappled with the “suicide” stigma. Community whispers of affairs were dismissed as gossip. For 17 years, the murders remained hidden, allowing the killers to prosper—Howell remarried after divorcing Stewart in 2009, while she resumed nursing.

Confession and the Unraveling Investigation

The breakthrough came in 2009, when Howell, gripped by religious fervor during a church retreat, confessed to church elders about the murders. Pressured by his third wife, he approached police in May 2010. Detectives reopened both cases, finding Howell’s detailed admissions corroborated by overlooked evidence: drug residues in Lesley’s system mismatched suicide norms, and heater flue blockages matched both scenes.

Hazel Stewart was arrested in 2010. Initially denying involvement, she cracked under interrogation, admitting complicity but claiming Howell coerced her. Forensic re-examinations confirmed the staging—chimney sweeps verified deliberate blockages, and witness statements recalled suspicious behaviors. The Police Service of Northern Ireland’s Historical Enquiries Team pieced together timelines, proving joint planning via phone records and diaries.

The Trial: Justice After Two Decades

Hazel Stewart’s trial began in March 2012 at Belfast Crown Court. Prosecutors portrayed her as an equal partner, citing her active role in Trevor’s murder and endorsement of Lesley’s. Key evidence included Howell’s testimony—he received an indeterminate sentence for manslaughter—and Hazel’s own words from prison letters, boasting of their “perfect crime.”

The defense argued Hazel was manipulated, a victim of Howell’s dominance. But jurors saw through it, convicting her on May 14, 2012, of manslaughter for both deaths. Judge Paul Girvan sentenced her to a minimum 18 years, stating her moral culpability matched Howell’s. She appealed unsuccessfully, remaining incarcerated at Hydebank Wood Women’s Prison.

The verdicts brought closure. Lesley’s brother-in-law, Victor Howell, called it “justice at last,” while Trevor’s sister Emily McBride honored his memory: “Trevor was no suicide; he loved life.”

Psychological Underpinnings: Love, Control, and Denial

Experts analyzing the case point to narcissistic traits in both perpetrators. Howell exhibited god-complex delusions, believing divine sanction for his acts. Psychological profiler Dr. Samantha Lundrigan noted their folie à deux—a shared psychosis where obsession justified murder. Stewart’s nursing background provided detachment, treating deaths clinically.

Denial sustained them: Howell rationalized via religion, Stewart via victim-blaming. Studies on spousal murder-suicide staging, like those in the Journal of Forensic Sciences, highlight how such duos exploit trust. Their remorse surfaced only under threat, underscoring superficial contrition.

Legacy: Reforms and Victim Remembrance

The Howell-Stewart case spurred changes. Northern Ireland mandated advanced carbon monoxide detectors and refined poisoning protocols. It inspired media like the BBC’s “The Secret” documentary, raising awareness of “perfect murders.” Victims’ families founded support groups, advocating for cold case reviews.

Today, memorials honor Lesley and Trevor. Lesley’s children forgave Howell publicly in 2016, a testament to resilience. Stewart, now 59, remains imprisoned, her parole bids denied amid victim opposition.

Conclusion

Hazel Stewart’s gas-staging murders with Colin Howell stand as a grim chapter in true crime, where domestic bliss concealed lethal intent. Their story underscores forensic evolution and the enduring pain of betrayal. Lesley and Trevor deserved better—lives cut short by those they trusted most. As society reflects, it honors the victims, ensuring such deceptions face scrutiny. Justice, though delayed, affirmed truth’s power over lies.

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