Mental health staff treating an ex-Royal Marine who killed a dog walker warned police about him.
Peter Wrighton, 83, from Banham, was stabbed repeatedly to the back of his head and neck and through his left eye in an attack which left his head almost severed from his body.
A jury took less than an hour on Wednesday to find former soldier Alex Palmer, 24, guilty of murdering Mr Wrighton as he walked his dogs in woodland near East Harling on August 5 last year.
Palmer, of Freesia Way, Cringleford, will be sentenced at Nottingham Crown Court today.
Speaking after the verdict yesterday, Mr Wrighton's family said they were 'shocked, astounded and angered' at revelations relating to Palmer's mental health.
The court had heard how Palmer suffered mental health problems following a head injury from being attacked on a night out in Plymouth in 2013.
He told mental health professionals about voices in his head which told him to hurt people, particularly dog walkers.
Staff at mental health service, the Norfolk and Suffolk Foundation Trust (NSFT), then flagged their concerns to police.
A spokesman for the NSFT said: 'Staff are encouraged to highlight circumstances where they are genuinely concerned an individual poses a real threat to themselves or to the safety of others.
'The Trust can confirm that staff did, on more than one occasion, liaise closely with other organisations including the police to raise concerns.
'Staff acted appropriately at all times with full and proper consideration to the safety of Mr Palmer as well as to the safety of others.'
'It should be remembered that this has been an extreme and rare situation.'
A serious case review is being held to see if lessons can be learned.
In a statement read outside court, Mr Wrighton's daughter Carol Todd and son Andrew Wrighton said: 'We have all been struggling to come to terms with losing him in such a way and our mum, his wife of 59 years, has been left bereft and lonely.
'However, the revelations of the evidence relating to the mental health of Alexander Palmer have shocked, astounded and angered us.
'We feel this should not have happened and mental health professionals failed him, his family and our family.
'My mum, brother, myself and our children not only feel grief but anger, as we believe this crime could have been prevented.'
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