A former Uruguay diplomat has admitted stabbing an LGBT rights campaigner to death following a "long-standing" neighbour dispute.
Enrique Facelli, 49, attacked Julian Aubrey at his home in West Kensington in October last year.
Police had been called to the flat in Shaftesbury Place on Warwick Road to reports of a man found with stab wounds.
Mr Aubrey, 55, was pronounced dead at the scene and a post-mortem later confirmed he had suffered multiple stab wounds.
His neighbour, Facelli, was due to face trial for his murder at the Old Bailey.
But at a hearing before Judge Anthony Leonard, QC, the defendant pleaded guilty to manslaughter by reason of diminished responsibility.
Prosecutor Tom Little QC said the Crown accepted the lesser charge in light of two psychiatric reports.
Mr Aubrey was formerly co-chairman of the Royal Borough of Kensington and Chelsea LGBT liaison group and in 2014 was recognised by the Princess Royal for his work counselling victims of sexual abuse.
Opening the case, Mr Little said: "This case involves a long-standing neighbour dispute.
"There were many years of allegations and counter-allegations between the neighbours."
They escalated to the point where the defendant showed "extreme signs of paranoia", the court heard Facelli had alleged the victim had "studied the dark arts" and was a devil worshipper.
Mr Aubrey had denied various accusations that he had opened the mail box, left faeces in the stairwell, and was trying to poison his neighbours with caustic soda.
In July last year, the defendant had forced his way into Mr Aubrey's home with a crowbar and axe, the court heard.
Then on October 30 last year, tradesmen found Mr Aubrey's body lying in the hallway of his flat. He had suffered 22 stab wounds.
Mr Little told the court the defendant was suffering from paranoid schizophrenia at the time of the killing.
In a victim impact statement, Mr Aubrey's sister said: "Julian did not deserve such an evil and horrific death."
She described him as a "kind, sensitive, gentle, sincere and caring" man who "could be too trusting and a little bit gullible".
Mr Aubrey had a difficult childhood but was intelligent and creative, with a love of painting.
She said he had been privileged to meet Princess Anne, who recognised his work as a counsellor in 2014.
In mitigation, Patrick Gibbs QC told how Facelli had been an intelligent individual who spent 18 years working as the cultural attache for the embassy of Uruguay in London.
But he had been in "mortal fear" of Mr Aubrey who he had complained about to police, housing and mental health authorities.
He spent money on a "forensic report" aimed at detecting bugging devices and air filters, he said.
He also moved out of his flat for nine months to get away from the perceived "persecution".
Facelli had been "driven quite out of his wits" and had been sectioned before the killing, Mr Gibbs said.