Both were slapped with a 12-month referral order to the youth offending team, were disqualified from keeping any animal for 10 years and ordered to pay £300 costs.
The dog involved in the case has also been subjected to a deprivation order and will be taken into RSPCA care until he’s ready for rehoming.
Sully’s owners became concerned after he had been missing from their home for a number of days.
They checked their CCTV camera for clues about where Sully may have gone – but they were confronted with images of their cat’s shocking plight.
One youth can be seen hitting the 13-year-old grey Bengal type cat from beneath a car with a stick, before the dog is set on him to catch and kill the defenceless pet.
The dog is held by the collar behind the car, before being released to chase Sully.
The footage shows the dog duly chasing Sully up the street, and – after attacking the cat on a number of occasions – mauls him to death.
Sully’s dead body was found in the bushes – after one of the offenders had tossed his remains away.
RSPCA inspector Gemma Cooper said: ‘The shock and horror I felt when I first witnessed this CCTV footage has remained with me.
This was a disturbing, harrowing and deeply sinister attack which would have caused immense suffering to poor Sully.
‘It is frightening to think two children would set out to do something so deliberately cruel. It appears the dog had been trained to kill like this.
‘We know most people across Merthyr and beyond will be disgusted by the treatment of an innocent, defenceless cat in this way.
This was a premeditated attack, seemingly done for the boys’ fun and pleasure, for which the RSPCA had to seek justice.
The actions of these individuals has left a family broken and without their beloved pet cat and family member of 13 years.’
Sully’s owner – who wishes to remain anonymous – added: ‘We are absolutely heartbroken.
‘Sully was so happy, and was a member of our family. His killing by these cruel people brings shame to Merthyr Tydfil. This was a heinous act.
‘He was well-known and popular in the local area – always sitting on the path he’d get petted and fussed by people walking along the lane and regular dog walkers all knew him.
He’d regularly sneak into a neighboring dental practice, and make friends with patients in the waiting room. Sully was a real character and was loved by all who met him. He was harmless and had never hurt anyone.
We all miss him so, so much. It was so strange for Sully to be missing. He’d gone to follow family members to the local park and was out and about as usual – but didn’t come home that day.
We started to get worried, so I checked our CCTV cameras – and saw these boys walking with a dog and that’s when it all happened.
‘It was horrifying to watch. I was screaming at the screen for Sully to run for his life but the dog was just too fast for him.
‘What I witnessed that day will never leave me – it was like watching one of my children being attacked.
Sully was 13 years old and was one of our family members who spent every night curled up on our children’s beds and his senseless killing has affected them deeply.
‘Telling my wife and children he was dead was so, so hard. I will never forget watching the offenders revel in what they did, and will never forgive them for what they have done to us.
They threw poor Sully’s body into the bushes like a piece of junk; and I had to go and get the body, and get him cremated, to get some dignity for him.
It was one of the hardest things I’ve ever done.’