A teenager from Abercynon, near Pontypridd, has been found guilty of murdering a 64-year-old widower in his own home last January.
Cardiff Crown Court heard that following a blundered robbery Bleddyn King was left covered in his victim's blood after the brutal attack in his home in Pentyrch.
King had planned to rob pensioner David Evans but stabbed him so ferociously his knife blade was bent.
The court also heard how the teenager stabbed Mr Evans' cat to death before setting his bungalow on fire and made off in his victim's car.
When police stopped the car King was found to have two bank cards belonging to Mr Evans.
The court heard how Mr Evans was just 5ft 6in tall and weighed eight-and-a-half srone compared to King who has a "muscular and powerful physique".
Bleddyn King will return to Cardiff Crown Court tomorrow afternoon for sentencing.