Exeter Crown Court heard that a depressive psychosis led Richard Young, 53, of Launceston, Cornwall, to attack his wife Lynda at Dartmoor on 27 March this year.

James Tabor QC, prosecuting said Mrs Young, also 53, fought back in vain as her husband tried to strangle her then repeatedly stabbed her in the face and body before finally using a granite boulder to fracture her skull.

The jury acquitted Young by reason of insanity.

'An absolute tragedy'

The judge, Mr Justice Sedley, ordered that Young be detained indefinitely in a secure mental hospital.

Passing sentence he told Young: "This is not a case for punishment. If it were, no punishment could be as dreadful as the one you are undergoing.

"You are now in better mental health and you are aware what you have done. You have killed the wife you loved and who loved you."

Howard Godfey QC, defending, told the jury that five psychiatrists agreed Young was for the purposes of the law insane at the time of the offence.

After the case, Detective Inspector Bob Brown said: "It is an absolute tragedy which has struck the family."

Speaking on behalf of the couple's two adult sons, he added: "They have lost a mother, and now have severe problems with their father's mental illness."

Poster eyes

After his arrest Young told a consultant psychiatrist that shortly before the killing he could see his wife's eyes had become red.

"He likened this to the Tory poster of Tony Blair when they pictured him as the devil," Dr Angela Roundsfield told the court.

Mr Tabor said Young suffered from a transient form of depressive psychosis which, when it re-appeared in late 1997 after a lapse of many years, was to have "the most tragic of consequences".

The day before the killing Young drove to Dartmoor intending to commit suicide, but failed to do so and drove home to tell his wife what he had done.

Next morning he telephoned the police. However, his wife took the phone from him and told the police she wanted no police involvement, saying she thought he was unwell.

On 27 March, as the couple drove to a doctor's appointment, Young turned off the road leading to the surgery and killed his wife in broad daylight, with passers-by witnessing what happened.