A KILLER who stabbed a hillwalker in a random attack had experienced a build-up of anger as his "severe" mental disorder deteriorated, a consultant forensic psychiatrist has told a court.

Dr Dinesh Maganty told jurors he believed the "significantly impaired" psychotic condition of Moses Christensen was the only explanation for the killing of 70-year-old Richard Hall.

Jurors at Stafford Crown Court have been told they must decide whether Christensen is guilty of murder or manslaughter by reason of diminished responsibility.

Prosecutors allege privately-educated Christensen was able to understand the nature of his conduct, formed rational judgments and killed Mr Hall last August on Shropshire's Brown Clee Hill "because that is exactly what he wanted to do".

Giving evidence from the witness box on the fourth day of Christensen's trial, Dr Maganty cited examples of what he said were irrational actions, including the 22-year-old's "worse than curious" eating habits and his desire to be a "lone soldier" in the Royal Marines.

Answering questions from defence QC Anthony Metzer, Dr Maganty said Christensen had been transferred from a prison and was being treated at Ashworth Hospital in Merseyside.

Giving details of a report into his assessment of Christensen, the psychiatrist told the court: "When it came to 2020, clearly things were deteriorating very rapidly.

"There are a number of examples of his irrational behaviour.

"I think it's best put by the recruitment army officer who said he (Christensen) thought he had the skills... although he didn't have any of the skills.

"He had lost touch with reality, there is no doubt about that.

"He is clearly suffering with a severe mental illness and a severe mental disorder... he is getting more and more angry.

"The anger was building because he just could not see that his irrational actions were not rational."

Christensen, of Corser Street, Stourbridge, West Midlands, is said by friends and family members to have appeared depressed and suicidal in the previous weeks, after abandoning plans to kayak around the UK.

Asserting that there was absolutely no doubt Christensen had an abnormality of mental functioning, Dr Maganty added: "The whole sequence of events leading up to this were irrational.

"Ultimately it is for the jury to decide what is rational... but I would not see his actions of going around the UK in a kayak, with no seafaring experience and with a dog in it, as rational.

"His level of detachment from reality was growing."

Jurors were also told Christensen would be "disadvantaged" by giving evidence and is currently detained under a section of the Mental Health Act which requires him to receive urgent treatment in a secure hospital.

Asked by Mr Metzer if Christensen's mental state would have impaired his ability to exercise self-control, Dr Maganty said: "There is no doubt that affected very substantially his ability to think rationally.

"Frankly, other than his mental disorder there is no other rational explanation for what happened. If he wasn't mentally disordered there would not have been a death.

"In the months leading up to the killing he was increasingly disordered. It is quite clear he was becoming psychotic and acting in a psychotic manner.

"The only explanation for this killing is the mental disorder.

"This was not something that happened out of the blue. There is a long lead-up to it and the evidence of that lead-up is there for all to see."

The trial continues.