A former Royal Marine, who killed a dog walker in Norfolk woodlands, suffered with mental health problems after being attacked by his colleagues on a night out.
Alexander Palmer had serious head injuries from the attack in Plymouth in 2013 which had a 'catastrophic' effect on his mental health, police said.
Detective Superintendent Marina Ericson, who was the senior investigating officer in the case, said Palmer's mental health problems were triggered by the attack from his fellow soldiers.
The 24-year old from Cringleford was convicted on Wednesday of killing dog walker Peter Wrighton in woods near East Harling in August 2017.
The trial of Palmer heard how since the head injury he experienced hallucinations with voices in his head, which Palmer dubbed Alex or Little Alex.
The voices told him to hurt or kill strangers, particularly dog walkers.
He left the army in 2015 but his career should have turned out very differently. He dreamed of becoming a soldier like his grandfather.
The former Old Buckenham High School pupil joined the Royal Marines in mid-2013.
As a 16-year-old he received an A-grade pass to become a paratrooper with the British Army.
Speaking when he was 16, Palmer said: 'I want to be a paratrooper. If you're going to be in the army, you might as well be the best.'
He received the top grade after a gruelling physical and psychological selection process.
He passed a psychometric test and a medical course to test mental and physical ability and formal interview.
He was then sent to the Army Development Selection Centre training camp for two days and nights of medicals, tests and interviews.
Palmer went onto start his training at the Army Foundation College in Harrogate, north Yorkshire, in September 2010 and spent a year learning team leadership skills and IT skills, as well as adventure sports training and basic training.
He then moved onto Catterick for 14 weeks of infantry training and four weeks of parachute jumps at Brize Norton.
The young Palmer impressed those that taught him.
Palmer had wanted to become a paratrooper after helping out at a skydiving school at Old Buckenham Airfield, near Norwich.
Of his first jump, he said: 'I loved every minute…Some of the guys at the airfield were ex paratroopers and they told me about their exploits.'
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