A 15-year-old boy stabbed another teenager to death in a flat they were using to sell heroin and crack cocaine from, a court heard today.

Koy Bentley, 15, was stabbed twice in the chest by the other youth as two young women they’d just sold drugs to were in a bedroom taking them, it was claimed.

The fatal knife wound passed through Koy’s ribs, into the chest cavity, through the lower left lung and into his heart, a jury was told.

The teenage,r alleged to have inflicted the fatal wound, then fled the flat in Rainbow House in Water Lane, Watford, with a 21-year-old man.

He is later said to have disposed of the kitchen knife under a bush in an alleyway.

The trial began at St Albans Crown Court today.

The teenager, now 16, pleaded not guilty to murdering Koy, from Watford, on the afternoon of June 5 last year.

Outlining the case to the jury prosecutor William Harbage QC said: “This case is about the death of a 15-year-old boy.

"He was stabbed to the chest, murdered by this defendant.

“The two knew each other and maybe were even friends, but the evidence suggests a disagreement suddenly arose between them and the accused stabbed Koy Bentley not once, but twice in his chest.”

“The background to all this is drugs.”

He told the jury of five men and seven women that Koy, the accused, and another young man, aged 21, were all involved in supplying class A drugs.

The court was told the three were operating from a flat at Rainbow House in Water Lane, Watford.

On the afternoon of June 5 last year, two young women, who earlier had bought drugs at the flat, returned to buy more.

To fund their purchases, they’d been shoplifting in Watford town centre and on arrival at the flat exchanged goods they’d stolen for more drugs.

With the drugs, the women went into a bedroom at the flat leaving the accused, Koy, and the 21-year-old man in the open plan kitchen/dining room area.

The prosecutor said the older man suddenly heard Koy saying to the other teenager “Don’t hold me like that, nobody holds me like that”.

He said the man looked up to see the accused holding Koy with one hand around his neck and he told the pair to “chill out”.

The man looked away, but then heard the sound of a blow.

Mr Harbage went on: “He looked up to see the accused holding a knife in his hand with blood on the blade.

"Koy had been stabbed to the left side of his chest.

"After that there was panic."

The court was told the defendant and the 21-year-old fled along with one of the young women.

Her friend, who she had been taking drugs with in the bedroom, remained and made a 999 call to summon an ambulance.

The prosecutor told the jury: “You may be shocked that Koy could be involved in selling crack cocaine and heroin at the age of 15, but plainly he did not deserve to die.”

The accused, from north London, has pleaded guilty along with the 21-year-old man to a charge that they conspired together, and with Koy, to supply a controlled drug of Class A.

The 21-year-old man, who cannot be named for legal reasons, has also pleaded guilty to perverting the course of justice by instructing one of the women who was at the flat that afternoon to lie to the ambulance crew about how Koy had received his injuries.

He also told the other girl she should return to the flat and remove any incriminating evidence.

The jury was told that the accused and the 21-year-old man had met through Instagram and would talk about how they “could make money”.

Mr Harbage said they decided on drug dealing, and Koy Bentley, who had been involved in selling drugs, eventually joined the conspiracy after he told them he knew of the flat in Rainbow House where they could operate from.

He said those who had previously used it to deal from had left 30 wraps of crack cocaine there.

The court heard the plan was to sell the wraps at £10 a time and use the money they made to buy more “stock”.

A mobile phone was acquired and the number given out to would be buyers on the street.

Mr Harbage said Koy and the accused would stay at the flat to sell the drugs.

“All three had conspired to deal Class A drugs together,” he said.

Mr Harbage said in the flat banter would often pass between Koy and the defendant with them saying: “Shut up or I’ll stab you”.

He added: “You may think that it was an unfortunate phrase in view of what happened later.”

The court then heard that after Koy had been stabbed he didn’t at first appreciate what had happened.

Mr Harbage said: “Koy didn’t seem to realise he had been stabbed.”

He said the teenage stood up and lifted his top and realised there was a lot of blood present.

The case continues.