Leslie Winnister, 69, bludgeoned to death wife Suzanne with a marble chopping board at their home in Bexley, south-east London last September.
The court heard he was gripped by psychotic delusions at the time of the killing, including suspecting his wife of dealing in occult magic, poisoning his food, and tampering with his car.
Their marriage, which was already under strain thanks to Winnister’s deteriorating mental health, became “intolerable” during the Covid-19 lockdown.
The court heard he killed Mrs Winnister just days after seeing a nurse who mistook his symptoms for possible dementia and deferred consideration of his case for a week.
A police medic had also missed signs of the danger when Winnister had been arrested on suspicion of violently attacking the handyman.
Dr Nigel Blackwood, who carried out a psychiatric assessment of Winnister after the killing, said “limitations” on the medical services he interacted with meant the dangers he posed to his wife were missed.
“They saw a man very close to retirement, employed for 40 years, white middle-class, with no criminal history, and their anxieties would not have been provoked”, he said.
“Of course it is entirely to be regretted that he wasn’t assessed by a psychiatrist who would have recognised the dangers inherent in the case.”
Winnister pleaded not guilty to murder but admitted manslaughter by diminished responsibility, and was today detained indefinitely in a secure hospital for mental health treatment.
“Not only was this man palpably ill but everyone knew it”, said Judge Wendy Joseph QC.
“I am satisfied Leslie Winnister was and continues to suffer from mental illness.”
Mrs Winnister’s best friend, Beverley Johnson, told the court in an impact statement: “I feel Les has taken away our future together, to grow old as companions.
“She was just lovely, she was my best friend and I loved her very much.”
The court heard Winnister’s unfounded suspicions about his wife’s fidelity began in late 2019 when she penned a text to their handyman, Alf Mainwaring, saying: “Are you coming today? x”, but mistakenly sent it to her husband.
She told Winnister the kiss was a “casual gesture” she often sent to people, but this was the “likely genesis of the defendant becoming convinced that his wife and Alf were having an affair”, said prosecutor Bill Emlyn Jones QC.
“In the spring and summer of 2020, particularly once the nation was in lockdown after the outbreak of the Coronavirus pandemic, the relationship between the Winnisters became intolerable.
“His paranoia led him to accuse her regularly of infidelity, and of trying to kill him by poisoning his food.”
The court heard Winnister beat Mr Mainwaring over the head with a crowbar in August 2020 when he came to fix their freezer, but did not face prosecution.
The incident led to Winnister moving out of the family home to a nearby Holiday Inn for five weeks, as his wife told friends she was scared for her safety.
Occasionally they met for meals, but Winnister continued to harbour believes that she was “interfering” with his car and credit cards, and “attempting to poison him with carbon monoxide in his hotel room”, said the prosecutor.
Attempts were made to refer Winnister for psychiatric assessment, and he went to A&E while saying he felt unwell but the danger he posed was again missed.
“It seems that Mrs Winnister was extremely upset by her husband’s condition, and was concerned that whilst at the hotel he was not eating properly, or looking after himself”, said Mr Emlyn Jones.
“He began to appear unkempt and was losing weight. She eventually decided to let him back into the house, although it was clear to her friends that she was very uneasy about doing so. She had a lock fitted to her bedroom door.”
The killing happened on September 8 last year, just two days after he had moved back into the family home.
A friend found Mrs Winnister’s body on the kitchen floor, while the killer was found at a local pub with a pint of lager and a packet of crisps.
He admitted having blood on his clothes, and commented: “I’ve just had a terrible day.”
Winnister will be held in a secure hospital for treatment, which is expected to last for several years.