Detectives are reviewing the deaths of a convicted murderer’s father and grandfather in case he killed them and avoided detection, the BBC understands.

Luke D’Wit, 34, was jailed for a minimum of 37 years in March after he used the opioid painkiller fentanyl to poison married couple Stephen and Carol Baxter in West Mersea, Essex.

Police are now exploring whether D’Wit was responsible for the death of his father, Vernon, who had been prescribed fentanyl before he was found dead at his home in 2021.

Officers “will not hesitate to act” if they uncover fresh evidence, an Essex Police spokesman said.

Due to the subtle nature of poisoning, police are keen to establish if D’Wit killed anyone else before he was caught and jailed.

As part of their review, detectives have also been re-examining how D’Wit’s grandfather came to die.

Det Supt Rob Kirby previously told the BBC he had “absolutely no doubt” D’Wit would have committed further murders had he not been caught.

He said he could not rule out the possibility D’Wit had already killed others before being convicted of murdering the Baxters.

Det Supt Kirby described the killer as “one of the most dangerous men” he had seen during his career.

Vernon D’Wit was found dead in a chair at the family home in West Mersea in 2021.

Mr Baxter, 61, and Mrs Baxter, 64, were also discovered unresponsive in their armchairs at their Victory Road home on Easter Sunday 2023.

Motivated by a “desire to control” them, D’Wit had manipulated the couple for two years before he laced their medication with a fatal dose of fentanyl and rewrote their will.

He had extracted the fentanyl from patches originally prescribed to his father, the trial at Chelmsford Crown Court heard.

Mr Justice Lavender said following the death of D’Wit’s father, the murderer had retained the drug “in abundance”.

A haul of the powerful opioid painkiller was found in a backpack at the home D’Wit shared with his mother in Churchfields, West Mersea.

“Up to the conviction and sentence of Luke D’Wit, our determined focus has been securing justice in relation to the murders of Carol and Stephen,” the police spokesman said.

“As with any investigation of this magnitude, everything we have uncovered is being reviewed and should anything suggest this has been the case we will not hesitate to act.”

The trial heard D’Wit had befriended the Baxters after Mrs Baxter employed him for her shower mat business Cazsplash.

He went on to create more than 20 personas to manipulate her into drugging herself with medication she was told would help her better manage the autoimmune illness she had been diagnosed with, Hashimoto’s disease.

However, the medication contained strong doses of promethazine and repeated use over two years left Mrs Baxter with dementia-like symptoms not associated with Hashimoto’s.

D’Wit later administered a lethal dose of fentanyl to both Mr and Mrs Baxter on Good Friday that year and watched them die via hidden cameras.

The judge said it was the conclusion of a “cruel and senseless” campaign fuelled by control.

Reading her victim impact statement at court, the couple’s daughter, Ellie Baxter, said “it was like my insides were on fire” when she discovered her parents’ bodies.

She described D’Wit as “a man so manipulative he hacked his way into our lives over a decade ago, schemed and thoroughly planned my parents’ demise”.

Speaking to the BBC in March, Det Supt Kirby said D’Wit’s downfall was “the arrogance that existed within him”.

He said once the fentanyl link was established following toxicology tests of Mr and Mrs Baxter’s bodies, the trail led straight back to D’Wit.

“D’Wit went to great lengths to cover up his tracks. He deceived everyone who knew him,” he added.

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