A teenager murdered his stepmother with a samurai sword and an axe after becoming "deadened" by online beheading videos, a court heard.

Rueben Brathwaite, 17, developed an interest in "murder, death and mutilation" while looking at American website 4chan before he launched his attack on Fiona Scourfield, 54, a charity worker, Swansea Crown Court was told.

On the day of the killing in March, Brathwaite had a cup of tea with his stepmother after a "normal day at school", then lured her outside their home on a farm in Carmarthenshire by saying that her cat had been injured. He attacked Scourfield, causing "catastrophic blood loss".

Brathwaite then called 999 and said he had hit his stepmother with the blunt side of an axe and used the samurai sword to slash her throat.

Prosecutor John Hipkin said the teenager told the call handler: "There's no sign of life. I hit her eight or nine times in the head with an axe.

"I'm just fed up with my life and I wanted to commit suicide but couldn't bring myself to kill myself.

"Then I just thought that if possible I would kill someone else."

Brathwaite took photos of Scourfield's body and unsuccessfully tried to upload them to the internet as a "confession". The victim, a leading member of the charity UK German Shepherd Rescue, died from blunt injuries to her skull and severed arteries.

Brathwaite, who was 16 at the time of the killing, went to live with his father and Scourfield in June 2013 after difficulties in the relationship with his mother. Psychiatric reports showed he had no mental health conditions when he committed the crime.

He admitted murder. Paul Hobson, defending, said his client showed remorse in a letter he wrote.

Judge Mr Justice Simon Picken sentenced Brathwaite to life with a minimum term of 15 years.