Jamie Yeates, a promising jockey, was stabbed as he slept
A 42-year-old man has been found guilty of murdering his stepson by stabbing him 18 times as he slept in his bed.
Carl Wayne Bowen, from Llanelli, had admitted killing promising jockey Jamie Yeates, 15, but denied murder on the grounds of diminished responsibility.
The jury at Swansea Crown Court found him not guilty of the attempted murder of Kimberly Yeates, Jamie's sister, but guilty of wounding with intent.
He was also found guilty of the attempted murder of their mother Maria.
Sentencing will take place at 1030 BST on Wednesday.
The guilty verdicts followed a three week trial in which the jury heard Bowen was a "possessive, controlling and manipulative man" who refused to feed Jamie and encouraged his other children to assault him.
He would go for months without even talking to him, the court heard.
The jury was told Bowen had banned his wife, a care home worker, from speaking to her own parents.
Carl Wayne Bowen was convicted of murdering his stepson Jamie Yeates
He continually suspected her of having affairs and she was not allowed to leave their house without his permission.
He timed her visits to the supermarket, checked her mobile telephone and examined the mileage on the family car.
Jamie and his sister Kimberley, now 19, had both been banned from having any contact with their father's family.
But when Jamie's grandfather developed cancer the two got back in touch and Jamie began visiting.
The jury was told how Bowen had spent 7 January drinking gin and orange.
In was during the early hours of the following morning, that he suddenly went to Jamie's bedroom with a kitchen knife.
Prosecutor Elwen Evans QC said what followed was a "brutal and vicious assault" on a sleeping, defenceless 15-year-old boy, who bled to death.
The court heard that the blows severed his spine and several ribs.
Ms Evans said Kimberley and her mother heard Jamie shout one word, "Mam".
The jury was told that on the tiny landing outside, Bowen then stabbed Kimberley twice in her arm and tried to head butt and stab his wife, who managed to escape.
The defence case was that Bowen had been suffering from delusions that his children were not his and his wife was being unfaithful.
Peter Rouch QC urged the jury to acquit Bowen on the grounds of diminished responsibility.
But psychiatrist Dr Philip Joseph told the court it was more likely Bowen lost control, and did not become psychotic.
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