Two teenage rappers responsible for fatally stabbing Adam Chambers in the heart with a large combat knife have been jailed.

Mr Chambers, who was 30, was slaughtered after arranging to meet someone to sell them drugs at the back of a block of flats in Woolwich on June 13.

Dval Doh, 16, was seen laughing after the knife attack as he walked away with 19-year-old Felou Abadja.

The jury heard how the teenagers had wanted to rob the victim.

Mr Chambers was left with a wound 20cm deep and 7cm wide.

Old Bailey Judge John Dodd QC said: "The callous behaviour of both you throughout the events of that June day are breathtaking."

The judge said Abadja - known as TV - recruited and exploited Doh, despite the youngster showing "a degree of enthusiasm" in the events on the day of the killing.

He added Abadja appeared to have "no sense of moral compass". Doh had previously been expelled from school after being caught with a knife.

Abadja, from Eltham, was sentenced to 18 years in jail with an extended licence of four years.

Doh, from Charlton, was served with 12 years with an extended licence of four years and he will be sent to a young offenders institution.

Doh was also handed a two-year sentence for having a blade in public and a five-day sentence for possessing class A drugs.

Both were found guilty of manslaughter and possessing an offensive weapon.

They were cleared of murder.

The pair had been recording rap music in a Blackheath studio on the day of the killing, prosecutor Sarah Whitehouse QC told jurors.

Abadja called a minicab to take him to Troughton Road before 5pm to meet Mr Chambers.

CCTV shows Mr Chambers arriving on his moped before driving off 12 seconds later.

Doh had stabbed the victim before Mr Chambers escaped and then collapsed nearby.

Mrs Whitehouse told jurors: "Mr Abadja and (the youth) fled back to the minicab. They were talking and laughing but seemed in a hurry and said 'let's go boss' to the driver."

After his arrest in Eltham, Abadja admitted witnessing the attack but said he was metres away when the stabbing happened.

Doh was arrested days later and the weapon and class A drugs were found in his bag.

He told jurors he stabbed Mr Chambers in self-defence with the victim's own knife.

Mr Chambers' father Steven Chambers said in a statement read in court: "These people who think it's ok to take someone's life need to be off our streets so that they cannot inflict this pain on another living soul.

"I spend every day thinking why, why Adam?"

Mr Chambers' mother Jacqui Edmonds said her son was trying to earn money to pay rent arrears.

She added: "I will never get over losing him. I know my family never will."

Detective Superintendent Lee Watling, who led the investigation, said: "This was a vicious unprovoked attack on the victim who was unable to defend himself.

"I hope today's sentencing gives Adam's family some measure of closure and comfort."