jealous cage fighter has been found guilty of murdering his teacher ex and trying to kill a boy, 15, she was having sex with.
Ex-convict Paul Robson, 50, had blackmailed Caroline Kayll, 47, about her relationship with the teenager for £35,0000.
He snooped on both of them outside her home in Linton, Northumberland, last November, and then attacked both of them.
A court heard how he kicked Mrs Kayll in the head while wearing heavy work boots, chopped off her hair in clumps and slashed her buttocks.
She was left with catastrophic brain injuries and couldn’t survive.
Robson also repeatedly attacked the boy with scissors and a meat cleaver, sprayed them both with ammonia and stole their phones – later updating her social media, pretending to be her, while he was on the run, Newcastle Crown Court was told.
Nicholas Lumley QC, prosecuting, branded him ‘a cruel and calculating coward’.
He said: ‘He was never going to do anything other than ruin her.
‘If his fury and his frustration got the better of him then he was going to take things further and end her life.’
The cage fighting coach and former MMA fighter denied murder, claiming it was the boy who attacked Mrs Kayll, and said he struggled to get the better of the less powerfully-built teenager in the ensuing brawl.
Robson had a clandestine relationship with Mrs Kayll while he was behind bars in HMP Northumberland.
They lived together but split up weeks before the murder and he blackmailed her when he found out about the illegal relationship she had started with the teenager, who cannot be identified.
Mrs Kayll was married to a senior prison officer when she started a clandestine relationship with Robson when he was serving at HMP Northumberland where she taught.
She had previously worked as a social worker, a police officer in Cumbria, a prison officer, took on a teaching role behind bars, then moved into a school role, Newcastle Crown Court heard.
Robson claimed he had a secret relationship with her during two jail stints, the second of which continued after he was released.
Mr Lumley told the jury that Robson had a hold over her when he found out about she was having sex with an underage boy, saying: ‘
He knew things about her which she would not want to be made public.’
She confided in a friend that Robson was blackmailing her for £35,000 and that her ex was ‘going to ruin her’ and tell her school, the jury heard.
Over 10 days in November, she transferred £29,000 to Robson and took out a £10,500 loan, having previously been solvent.
However, money was not enough for him, and on November 15, Robson drove three hours from Glasgow to Linton, having bought a locksmith’s bar, a magnetic GPS car tracker, screwdrivers, pliers, a wrench and the ammonia which he decanted into a washing-up liquid bottle.
CCTV showed him ‘prowling’ outside her house.
Witnesses heard a female voice shout ‘get out’ and later that evening Robson knocked on his former neighbour’s house to say ‘Caroline was in a bad way’, Mr Lumley said.
He then fled to Glasgow and remained at large while police made appeals to trace him before he was arrested.
He did not answer detectives’ questions but in a prepared statement said he was ‘broken’ by her death and claimed someone attacked him when he visited her home.