Benjamin Field, 30, was found guilty of killing 69-year-old Peter Farquhar, 69, in order to inherit his house and money after poisoning and gaslighting him.
Field was jailed for life with a minimum of 36 years in October 2019, by a judge who said he had killed his victim using a combination of sedatives, alcohol and possibly suffocation.
Mr Farquhar died in October 2015 but it was not deemed suspicious until Ann Moore-Martin, 83, alerted police that Field was poisoning her shortly before her own death in May 2017.
Police said Field had drawn up a list of 100 other people he could “use” for accommodation or money, and feared he would have killed again.
Field denied murder and is now appealing against his conviction, although he previously admitted entering fraudulent relationships with the pensioners to make them change their wills to his benefit.
His barrister, David Jeremy QC argued that the trial judge, Mr Justice Sweeney, misdirected the jury and the murder conviction was “unsafe” as a result.
At a hearing at the Court of Appeal on Thursday, he said the directions given to jurors before they started deliberations left the defence with “nothing to say” when in fact there was “much that could be said on Field’s behalf on the issue of causation”.
Mr Jeremy said the prosecution “could not prove causation” because there was “no evidence that Mr Farquhar had been forced or tricked” into consuming alcohol and a tranquiliser drug.
Oliver Saxby QC, representing the Crown Prosecution Service, said the murder conviction was safe and that drugs, alcohol and “smothering” were all part of a plan concocted by Field.
Benjamin Field, then in his 20s, with victim Peter Farquhar
Lord Justice Fulford, who heard the appeal with two other judges, said they will give their ruling at a later date.
Field admitted two counts of burglary and three of fraud before his murder trial, when he was found not guilty of conspiracy to murder Miss Moore-Martin and an alternative charge of attempted murder.
Two psychiatrists said Field was either suffering from a narcissistic personality disorder or a psychopathic personality disorder.
Prosecutors said Field had a “profound fascination in controlling and manipulating and humiliating and killing”, which was detailed in diaries and journals.
Sentencing him, Mr Justice Sweeney said Field “lived by deception and deceit and had been a well-practised and able liar”.
“You were able to build pressure on your victims to believe what you needed them to believe and then to do whatever you needed them to do,” he added.
The judge added that both victims were “lonely and craving for love and affection”, and were fooled into thinking Field truly loved them.
He met his first victim at the University of Buckingham, where Field was Mr Farquhar’s English student.
Oxford Crown Court heard that Field moved into Mr Farquhar’s home in the village of Maids Moreton in 2014 and in March of that year they underwent a “betrothal” ceremony at a church.
“It is one of the happiest moments of my life,” Mr Farquhar wrote in a journal. “Gone are the fears of dying alone.”
Ann Moore-Martin died aged 83 of natural causes, after being poisoned by Field previously
Less than two years later he was dead, a campaign of psychological torture that aimed to convince Mr Farquhar he was losing his mind.
Field spiked his food and drink with neat alcohol and hallucinogenic drugs, while moving everyday objects around the house and “gaslighting” his victim into believing he had misplaced them or forgotten his own actions.
Mr Farquhar, a well-known academic and author who had taught at Stowe and Manchester Grammar School, had been “fit in mind and body”.
But the court heard how Field’s efforts caused “agony” for his victim, causing him to believe he could be a closet alcoholic or suffering from dementia.
Mr Justice Sweeney said Field murdered Mr Farquhar by covertly giving him flurazepam and making him drink strong whisky, adding: “I have no doubt that, if it was necessary, you then finished him off by suffocating him in a way that left no trace.”
He attempted to portray Mr Farquhar, an eminent teacher and author, as an alcoholic in the hope his death would be attributed to natural causes after convincing him to change his will.
It was not until a second post-mortem in 2017 that police discovered Mr Farquhar had been given a cocktail of sedatives over several months, and may have been smothered.
Mr Justice Sweeney said Field then moved on to Ms Moore-Martin and used her loneliness, strong Catholic faith and love letters to manipulate her into changing her will after starting a sexual relationship.
The former headmistress triggered the police investigation by telling a friend he gave her “white powder” after being admitted to hospital, but later died of natural causes.
Before her death, Ms Moore-Martin told officers she changed her will because she thought she loved Field and “wanted to support him in all the ways I could”.
