A man who killed his best friend on Christmas Eve was experiencing psychosis “up to six months before the event”, a court has heard.

Dylan Thomas, 24, has admitted the manslaughter of William Bush, 23, at a house they shared in Llandaff on 24 December 2023, but has denied murder.

A forensic psychiatrist treating Mr Thomas for schizophrenia at Ashworth High Secure Hospital told Cardiff Crown Court he believed he was psychotic for months before stabbing his best friend.

The court heard Mr Thomas believed he could harness gravity and told police he was “exploring energy fields” when arrested for climbing a fence at Buckingham Palace on 6 November 2023.

Dr Panchu Xavier told jurors that his patient was experiencing psychosis when he was admitted to Ashworth in March 2024.

Mr Thomas was still undergoing treatment and was on anti-psychotic medication, he added.

“It has improved but he’s not completely free of symptoms,” said Dr Xavier.

He said that Mr Thomas’s family noticed changes in the months leading up to the killing, but not changes that most people would realise were signs of psychosis.

“He did say things that were odd,” he said, adding that “it wouldn’t have been obvious to lay people that he was psychotic”.

Mr Thomas met William Bush at school at Christ College in Brecon, Powys, and the pair had been friends since, the court heard.

While Mr Bush was popular, Mr Thomas had few friends and was viewed as something of a loner, said Gregory Bull KC, prosecuting.

Dr Xavier had spoken to Mr Thomas about his arrest on 6 November 2023 and he told him he had done this “because he was trying to explore energy fields between Buckingham Palace and Cleopatra’s Needle”.

A police officer said he rugby tackled Mr Thomas to the ground because he recognised he was unwell and did it in order to prevent him from being shot.

The court heard that, following his arrest, Mr Thomas did not recognise the gravity of what he had done and told police: “I’m over now, do you mind showing me round the palace anyway?”

Dr Xavier said Mr Thomas now “acknowledges that it was a silly thing to do”.

The court heard Mr Thomas believed he had the ability to harness gravity and wrote to Elon Musk telling him that “once you solve gravity, you can solve everything else”.

Defence barrister Orlando Pownall KC said there could be no question he was psychotic but said the area of dispute was “as to what time was there an area of psychosis”.

Mr Pownall told the court that his client had been through “a lot of stressful situations” including the separation of his mother and father and there was “alleged domestic violence”.

Dr Xavier said he did not report any psychiatric history, but there was reference to a maternal grandparent having mental illness.

He said the defendant had taken LSD in the past and had used cannabis, but it was not his view that drink or drugs played a role in the events of 24 December 2023.

The court also heard how searches were made on Mr Thomas’ phone for the anatomy of the neck, arteries, veins and Dignitas, which provides assisted dying services in Switzerland.

In his evidence, Dr Xavier said Mr Thomas had a view that he wanted to end his own life and had also looked up details of psychiatric wards in Cardiff.

“He was either thinking he wanted to end his life or get help,” he said.

Mr Thomas told the psychiatrist that he went upstairs and found Mr Bush armed with a knife and managed to disarm him, then repeatedly stabbed him in “self-defence”.

“My belief is he is describing what he believes happened,” he said.

Concluding his evidence, Dr Xavier said: “My view is very clear in my report, that he was psychotic before and I have no doubt he has schizophrenia.”

Mr Thomas denies murder and the trial continues.