Opportunities to treat a man who went on to kill his best friend following an attempted break-in at Buckingham Palace were missed, a court has heard.
Dylan Thomas, 24, is accused of stabbing William Bush, 23, 37 times in a “frenzied attack” on December 24 last year at their home in Llandaff, Cardiff.
Thomas admitted manslaughter by diminished responsibility at a previous hearing but denies murder.
He appeared before Cardiff Crown Court by video link from a psychiatric hospital on Monday.
The defence presented evidence from Dr Panchu Xavier, a consultant forensic psychiatrist at Ashworth Hospital Liverpool where Thomas is in custody.
Dr Xavier argued that Thomas, who is being treated for schizophrenia, was having a psychotic episode during the attack and had been for “up to six months before the event”.
This would include a period when he attempted to break into Buckingham Palace saying he was looking for “energy fields” between the palace and Cleopatra’s Needle.
The prosecution, who will be presenting evidence from their own psychiatrist, accept that Thomas is mentally unwell, but insist he planned the attack.
Dr Xavier said the attempted palace break-in was the first opportunity to realise something had been wrong with Thomas, but the psychiatrist who saw him speculated that he was autistic.
Thomas had climbed over the fence to the palace, where he was confronted by armed police who he told: “I’m over now so you may as well show me round the palace.”
He was ultimately rugby-tackled by an officer.
After the arrest he kept asking officers how they knew what he was thinking about.
The fact that you’ve got a young man who has climbed the palace gates and was nearly shot and his explanation for that is he was exploring the energy field would have made me want to ask further questions
Defence barrister Orlando Pownall KC said: “He wasn’t interviewed (by the police) because when he was seen by a psychiatrist he wasn’t considered fit for interview.
“The psychiatrist concluded that Dylan Thomas might be autistic.
“With the benefit of hindsight might it have been picked up at that time that he was psychotic?”
Dr Xavier responded: “Unfortunately that might have been the first time when an intervention could have happened that may have prevented him continuing to be unwell.
“His description of what happened, the manner in which he described it and I suspect some of the biases that clinicians have – the way someone is dressed, the fact that he was articulate – would in their minds make it easier for them to convince themselves that he was ok to go back to Cardiff.
“The fact that you’ve got a young man who has climbed the palace gates and was nearly shot and his explanation for that is he was exploring the energy field would have made me want to ask further questions.”
He also told the jury it would not have been obvious to a “lay person” that Thomas was psychotic.
The court heard that Thomas believed he had the ability to harness gravity and had written a message to tech entrepreneur Elon Musk, saying “once you solve gravity, you can solve everything else”.
He told the psychiatrist he had learnt everything about gravity in five months using Wikipedia and Google’s Bard AI chatbot.
The jury also heard he had a suspected auditory hallucination while in Primark, which caused his ears to ring for some time.
Rather than seek medical attention, Dr Xavier said Thomas had gone to a solicitor in an attempt to sue the store.
Mr Pownall said the defendant had been through “a lot of stressful situations” in his life, with his parents having separated when he was young and “alleged domestic violence”.
The trial continues.
