A GP has admitted plotting to kill his mother's long-term partner by disguising himself as a community nurse and poisoning him with a fake Covid booster jab.
Thomas Kwan, 53, was on trial at Newcastle Crown Court and had initially denied attempted murder, but changed his plea after he heard the prosecution open the case against him.
Police initially thought the married father-of-one used the chemical weapon ricin to try to kill Patrick O'Hara, 72, at his mother's home in St Thomas Street, Newcastle, on January 22, but an expert believed a pesticide was more likely.
Kwan sparked a major emergency services operation when police found lethal chemicals stored in the detached garage at his home in Ingleby Barwick, Teesside.
The Sunderland-based GP had already pleaded guilty to administering a noxious substance, claiming he meant to cause no more than mild pain.
The Crown's case was that he meant to kill his mother's partner of more than 20 years, who developed a rare flesh-eating disease as a result of the jab in his arm.
The Hong Kong-born doctor had developed an "encyclopaedic knowledge" of poisons, the court heard, and he studied how to get away with murder, police discovered from analysis of his home computers.
Opening the case on Thursday, Peter Makepeace KC, prosecuting, said: "Mr Thomas Kwan, the defendant in the case, was in January of this year a respected and experienced medical doctor in general practice with a GP's surgery based in Sunderland.
"From November 2023 at the latest, and probably long before then, he devised an intricate plan to kill his mother's long-term partner, a man called Patrick O'Hara.
"On any view, that man had done absolutely nothing to offend Mr Kwan in any way whatsoever.
"He was, however, a potential impediment to Mr Kwan inheriting his mother's estate upon her death.
"Mr Kwan used his encyclopaedic knowledge of, and research into, poisons to carry out his plan.
"That plan was to disguise himself as a community nurse, attend Mr O'Hara's address, the home he shared with the defendant's mother, and inject him with a dangerous poison under the pretext of administering a Covid booster injection."
Kwan forged NHS documentation to set up the home visit, disguised himself, used false number plates for the journey to Newcastle and booked in to a city centre hotel using a false name.
Kwan's mother, Jenny Leung, named Mr O'Hara in her will to the effect that he could stay in her house in St Thomas Street, Newcastle, should she die before her partner.
That decision led to her having a strained relationship with her son, so much so that the police were called when Kwan burst into her home uninvited in November 2022.
Kwan was "money-obsessed", jurors heard, even installing spyware on his mother's laptop so he could secretly monitor her finances.
Last November, Kwan wrote to Mr O'Hara claiming to be a community nurse called Raj Patel and offered him a home visit.
Mr Makepeace said: "As, I suspect, would any of us, Mr O'Hara fell for it hook, line and sinker, he had not the slightest suspicion that this was anything other than a genuine NHS community care initiative which he warmly welcomed and was grateful for."
Kwan went to his mother's house in a long coat, flat cap, surgical gloves and wearing a medical mask and tinted glasses, and carried out a 45-minute examination on Mr O'Hara, and even checked his unsuspecting mother's blood pressure when she asked.
Kwan, in what the court heard was broken English with an Asian accent, told Mr O'Hara he needed a Covid booster, even though he had only had one three months ago.
Mr O'Hara shouted in pain when it was administered and Kwan quickly packed his equipment and left, reassuring his victim that a reaction was not uncommon.
The pain continued and Mr O'Hara began to suspect something had gone badly wrong.
The next day his arm had blistered and was seriously discoloured and medics at hospital were baffled.
He had developed the flesh-eating disease necrotising fasciitis and needed to have part of his arm cut away to stop it spreading, and spent several weeks in intensive care.
The fake nurse's movements were traced using CCTV and police were able to identify Kwan as a suspect.
Searches of his home in the executive estate where he lived revealed an array of chemicals such as arsenic and liquid mercury as well as castor beans which can be used to make the chemical weapon ricin.
Police found a recipe for ricin on his computer but Ministry of Defence poisons expert Professor Steven Emmett, although still not sure which poison was used, thought iodomethane which is commonly used in pesticides, was more likely.
