A church warden has been jailed for life after being found guilty of murdering a university lecturer following a sustained campaign of physical and mental abuse.

Benjamin Field, 28, was convicted in August of killing Peter Farquhar, 69, a retired teacher and part-time university lecturer, to inherit his house and money, and then trying to make his death look like an accident or suicide.

Field was given life imprisonment with a minimum term of 36 years by Mr Justice Sweeney at Oxford crown court on Friday.

Detectives branded Field a psychopath and said he would have posed an “ongoing danger to society” had he not been stopped.

After Farquhar’s death in October 2015, Field, a Baptist minister’s son, began targeting Farquhar’s neighbour, 83-year-old Ann Moore-Martin, a deeply religious retired headteacher. He wrote messages on her mirrors purporting to be from God.

After protracted deliberations, Field was cleared of charges of conspiracy to murder and the attempted murder of Moore-Martin, who lived a few doors away from Farquhar in the village of Maids Moreton. Moore-Martin died from natural causes in May 2017.

The judge Mr Justice Sweeney said Field “lived by deception and deceit and had been a well-practised and able liar”.

He added: “The evidence at trial clearly demonstrated grandiosity, a sense of superiority towards others, the exploitation of others to achieve personal gain, the need to belittle and humiliate others, fixation on fantasies of power and success, intelligence, a need for admiration from others and a sense of entitlement, together with an unwillingness to empathise with the feelings, needs and wishes of others.”

David Jeremy QC, the defence lawyer, said two psychiatrists had said Field had either a narcissistic personality disorder or a psychopathic personality disorder. “He was and is an intelligent and educated man and chose to apply those gifts towards the manipulation and humiliation of his victims, leading to the murder of Peter Farquhar and the degradation of Ann Moore-Martin and the causing of irreparable harm to their families and those close to them,” he said.

Prosecutors said Field had a “profound fascination in controlling and manipulating and humiliating and killing”, and they alleged he had plotted his crimes with a friend, Martyn Smith.

Smith, 32, a failed magician, was cleared of murdering Farquhar and of conspiracy to murder and the attempted murder of Moore-Martin.

During the trial, jurors were told of Field’s elaborate project of befriending elderly individuals who were vulnerable and lonely and then defrauding them by allowing them to think he was in a loving relationship with them. He encouraged them to change their will to benefit him and then began a devastating campaign of physical and mental torture.

Facebook Twitter Pinterest Ann Moore-Martin. Field was cleared of charges of conspiracy to murder and attempted murder. Photograph: Thames Valley police/PA

Field admitted to poisoning, gaslighting and defrauding Farquhar in order to get a better job and inherit his wealth when he died, and he told the court he had also deceived and manipulated Moore-Martin in a similar way. He accepted he had “psychologically manipulated” the pair but he denied any involvement in their deaths.

Field drew up a list of 100 future “targets”, including his own parents and grandparents, the court heard. He told the jury the “100 clients” file was not just a list of future targets but of people who could help him. The Crown Prosecution Service said the case was like a “plot from a novel”.

Field and Smith met Farquhar when they were students at Buckingham University. Field struck up a friendship with the university lecturer and began lodging with him. Oliver Saxby QC, the lead prosecutor, told the jury that Field saw that Farquhar was vulnerable, “and this was something from the very outset he decided to exploit”.

Field and Farquhar soon entered into a relationship and had a formal ceremony, which they called a betrothal ceremony. Like Farquhar, Moore-Martin was unmarried and had no children. Saxby told the court she was “fundamentally lonely”.

In a statement, the Church of England diocese of Oxford said: “The sentencing of Ben Field marks the conclusion of a long, complex and disturbing case. It’s clear that Ben Field manipulated everyone he came into contact with. We’re determined to learn what we can from this extraordinary case. The church and wider society needs to be ever more vigilant of those who can be made vulnerable by the likes of Ben Field simply because they are elderly or lonely.”