A 50 year old prisoner is being quizzed by detectives after a fellow inmate from Teignmouth was stabbed to death at Dartmoor jail.

Alexander Cusworth was attacked and sustained a knife wound at the prison on Thursday afternoon.

He was flown by air ambulance to Plymouth’s Derriford Hospital where he was pronounced dead following emergency treatment.

Detectives, including scenes of crime officers, have been carrying our investigations at the Princetown jail.

A 50 year old man was arrested on suspicion of murder and is in custody in Exeter where he is being interviewed, said Devon and Cornwall Police.

A Prison Service spokesman said 37-year-old Cusworth, of Barn Park Terrace, was a serving prisoner but could not comment further because of the police investigation.

Cusworth was jailed for eight years in May this year for attacking his landlord so savagely with a broomstick he spent eight days in a coma.

He had admitted wounding with intent. He attacked Patrick O’Reilly because he mistakenly believed he had called him a rapist.

He battered him around the head with the broom before walking into a police station to confess. Mr O’Reilly was found in a pool of blood at his home and ‘died’ on the way to hospital but was revived by an ambulance crew.

He suffered bleeding inside his skull, spent eight days on a life support machine and a month in hospital.

Cusworth was jailed for a total of eight years at Exeter Crown Court in May.

Judge Simon Carr told him: ’You handed out a brutal beating with a weapon with no justification at all. It continued over a significant period of time and caused life threatening injuries.’

Eleanor Purkis, prosecuting, told that hearing said Mr O’Reilly was putting Cusworth up at his home in Teignmouth as a favour after he lost his own accommodation.

Cusworth was due in court on the day of the attack but instead walked into Teignmouth police station at 8am and told them he had attacked the victim.

Miss Purkis said: ’He told the officers "I have just given him a good kicking because he called me a sex offender. He is lying face down on his floor and there is a lot of blood. I hope he is hurt because he called me a rapist."

’In interview he said the victim deserved it and he was lucky he had not killed him.’

She said Mr O’Reilly had not accused Cusworth of being a rapist and had no idea why he launched the unprovoked attack.

At the time Cusworth was supposed to be undergoing drug rehabilitation as a condition of an eight month suspended sentence passed at Exeter in September 2013 for threatening bus passengers on the Den in Teignmouth with a kitchen knife.

William Parkhill, mitigating, said Cusworth had long-standing mental health problems which have been made worse by his abuse of class A drugs.

He said he deserves credit for his guilty plea and for saving Mr O’Reilly’s life by going to the police station to raise the alarm.