A church warden who conspired to murder his elderly lover to benefit from his will had a list of 100 other potential targets.
Police fear Benjamin Field, 28, could have killed again if a woman had not told friends that he was giving her “white powder” before she died and sparked an investigation.
Detective Chief Inspector Mark Glover said Field had drawn up a list of 100 people he could “use” for accommodation or money.
“His own grandparents were on there, his mum and dad, his brother, his girlfriend, her mother,” he told The Independent.
“Some of them were elderly, they fitted the same profile as his victims - independent, living alone, affluent, no children.”
Det Ch Insp Glover, the senior investigating officer for the case, said that if Anne Moore-Martin had not raised the alarm before her death he could have poisoned more victims undetected.
“If it hadn’t come to light from Ms Moore-Martin and her niece, we may not know about it now and he could have quite easily moved on to other people,” he added.
The 69-year-old’s death in October 2015 was not initially thought to be suspicious, after Field fabricated evidence of alcoholism.
But after Ms Moore-Martin died in May 2017, Mr Farquhar’s body was exhumed and a second post-mortem discovered sedatives in his system.
Field’s trial heard that he had poisoned Mr Farquhar over several months, after persuading him to change his will to leave him £20,000 and a life interest in his home.
After meeting his victim as a student at the University of Buckingham, where Mr Farquhar was a part-time lecturer, Field moved in and they entered a relationship that culminated in a church “service of commitment” in March 2014.
“It is one of the happiest moments of my life,” Mr Farquhar wrote in his diary. “Gone are the fears of dying alone.”
Field later started drugging him with benzodiazepine sedatives and encouraging him to drink more, while gaslighting him to make him believe he was losing his mind.
Prosecutors suggested that Field could have smothered Mr Farquhar while he was incapacitated and placed an almost empty bottle of whisky next to his body.
He then turned his attentions to Ms Moore-Martin, a neighbour in the same village.
The court heard Field entered an “undoubtedly sexual” relationship with her while sending her love poems and writing messages on mirrors claiming to be from God.
Deeply religious Ms Moore-Martin, a former Catholic school headteacher, suffered a seizure and was admitted to hospital in February 2017.
The following month, she told her friend that she had been given “white powder” by Field to sleep better.
A police investigation started and Ms Moore-Martin went into a care home, where she later died from a stroke.
Before her death, she told officers that she changed her will because she thought she loved Field.
“I wanted to support him in all the ways I could,” Ms Moore-Martin said. “I suppose I wanted to please and satisfy him.”
Prosecutors said that in his journal, Field had listed “options” for killing her, including “electrical device, dehydration, stair, sex?, in the bath?...od on her prescriptions…church tower…sleep apnoea” and planned how to make the death appear natural or accidental.
Det Ch Insp Glover, of Thames Valley Police, said Field had taken “pleasure in inflicting pain, torment and mental torture” on both his victims.
“Peter thought he was losing his memory and his mind, but really Ben was hiding everyday objects and then would then find them some hours later,” he added.
“Both relationships were a complete pack of lies … he didn’t care about anybody except Ben Field.
“I’ve never seen anything like it before and I doubt I’ll ever see it again.”
Prosecutors told Oxford Crown Court that Field made “desperate attempts to get away with” murdering Mr Farquhar.
Oliver Saxby QC accused Field of being motivated by “greed and a willingness to inflict pain and suffering”.
"He is arrogant in the sense that he could get away with it, finding it amusing that he could get away with it,” he told the court.
"It is for greed, it is power greed, being clever greed - being the person that can carry it off."
Mr Saxby dismissed a cover story mounted by Field, who admitted fraud but denied murder and attempted murder, as the “stuff of farce”.
The jury was told the police covertly recorded conversations Field had while being transported to magistrates’ court, in which Field talked of "getting away with it".
Field, a Baptist minister's son, admitted fraudulently being in relationships with Mr Farquhar and Ms Moore-Martin as part of a plot to get them to change their wills but denied any involvement in their deaths.
On Friday, he was convicted of murdering Mr Farquhar.
The defendant, of Wellingborough Road in Olney, Buckinghamshire, had admitted four charges of fraud and two of burglary.
Field’s co-accused, 32-year-old magician Martyn Smith who had lodged in Mr Farquhar's home, was found not guilty of murder.
The pair were both cleared of a charge of conspiracy to murder Ms Moore-Martin and Field was also acquitted of her attempted murder.
Field's brother Tom, 24, a Cambridge University graduate, was cleared of a single charge of fraud over obtaining £27,000 from Ms Moore-Martin for a dialysis machine.