A churchwarden has been found guilty of murdering an author after tricking him into changing his will.
Benjamin Field, 28, manipulated 69-year-old Peter Farquhar for financial gain and tried to make his death look like an accident or suicide.
Field was also accused of plotting to kill Mr Farquhar's neighbour Ann Moore-Martin, 83, in the village of Maids Moreton but was found not guilty.
He was remanded in custody and will be sentenced at a date to be fixed.
At Oxford Crown Court, Field was also acquitted of the attempted murder of Miss Moore-Martin.
Mr Farquhar died in the Buckinghamshire village in October 2015, while Miss Moore-Martin, who lived three doors away, died in May 2017 from natural causes.
Field, a Baptist minister's son, admitted duping both Mr Farquhar and Miss Moore-Martin into fake relationships with him as part of a plot to get them to change their wills, but denied any involvement in their deaths.
The court heard Field had undergone a "betrothal" ceremony with Mr Farquhar and was in a sexual relationship with Miss Moore-Martin.
Prosecutor Oliver Saxby QC told the trial Field carried out a sustained "gaslighting" plot aimed at making Mr Farquhar question his sanity.
Mr Farquhar's drinks were topped up with bioethanol and poteen, a high strength Irish alcohol, and his food was laced with drugs, Mr Saxby said.
Mr Farquhar, who taught part-time at the University of Buckingham and had three novels published, suffered night terrors and hallucinations which he recorded in a handwritten journal.
His third novel A Wide Wide Sea, published in 2015, was dedicated to Field, who delivered the eulogy at his funeral.
Field's co-accused Martyn Smith, 32, of Penhalvean, Redruth, Cornwall, was cleared of murdering Mr Farquhar, plotting to kill Miss Moore-Martin, fraud and burglary.
Speaking afterwards, he said: "I am relieved that this ordeal is finally over...The lessons I take from this case are first and foremost to always be your own person and secondly to always choose your friends very carefully."
During the trial Field admitted drugging Mr Farquhar with benzodiazepines and hallucinogenic legal highs to "torment" him.
He told the jury he did it "for no other reason other than it was cruel, to upset and torment Peter - purely out of meanness".
But prosecutors said Field had a "profound fascination in controlling and manipulating and humiliating and killing".
After Mr Farquhar changed his will three times in two years to benefit Field, he "had to die", Mr Saxby said.
The court heard Field "suffocated him" when he was too weak to resist, and left a half-empty bottle of whisky in Mr Farquhar's room to create the misconception he had drunk himself to death.
'Calculating and ruthless'
In a statement read by police, Mr Farquhar's brother Ian said: "[Field's] actions have been unbelievably callous, and he has told lie after lie after lie in order to achieve his goals, deceiving everyone he met."
Senior investigating officer Mark Glover described Field as "cruel, calculating, manipulative, deceitful", adding: "I don't think evil is too strong a word for him."
Chris Derrick, from the Crown Prosecution Service, said: "He is clearly a very calculating and ruthless man who spent a great deal of time planning what he was going to do."
After the verdicts, journalist Michael Crick, who was taught by Mr Farquhar at Manchester Grammar School, tweeted: "It's so dreadful to think my dear friend and teacher Peter Farquhar was murdered in such an awful way by a man he loved and trusted so much."
Another former pupil of the school, David Scheinmann, directed 2013 film Believe and has said a headmaster character, played by Toby Stevens, was in part based on Mr Farquhar.
Miss Moore-Martin's niece Ann-Marie Blake paid tribute to her aunt, who she described as "a kind, gentle, beautiful soul, who touched so many lives, leaving behind a legacy of wonderful memories".
Judge Mr Justice Sweeney said it had been a "challenging case" for the jury, which took 77 hours to reach its verdict.
He remanded Field, of Wellingborough Road, Olney, in custody until sentencing at a date to be fixed and ordered a psychiatric report.
Field previously admitted four charges of fraud and two of burglary.
His brother Tom Field, 24, of the same address, was cleared of a single charge of fraud.