The teenager said to have stabbed to death a 15-year-old boy at a Watford flat where they were selling heroin and crack cocaine has told a jury the murder was carried out by someone else at the property.

The 16-year-old, who cannot be named for legal reasons, denies murdering Koy on the afternoon of June 5 last year at a flat at Rainbow House in Water Lane, Watford.

The prosecution alleges that Koy, the accused and the man were involved in selling class A drugs from the flat.

He told St Albans crown that the murder was carried out by a 21-year-old man who was in the flat last June and part of the conspiracy.

The boy claimed the man stood in front of Koy, who was in a swivel chair, and suddenly stabbed him twice.

The jury has been told one of the wounds proved fatal and Koy, who lived in Watford, died in the flat.

Earlier in the trial the man, who is now 22 and who admits conspiring with the defendant to supply heroin and crack cocaine, told the jury how the three of them had been sitting in the lounge of the flat when the 16-year-old stabbed the boy.

The man, who cannot be identified, told the jury that the 16-year-old “had a knife in his right hand. It was a stainless steel knife”.

He went on “It had blood on it...on the tip of the blade. His arms were by his side.”

During the trial the jury have been told that, at the time of the murder, two women who had just bought drugs from the three were in a bedroom taking them.

The prosecution says there was a sudden disagreement between the accused and Koy in the lounge area of the flat that afternoon and that sparked the violence.

After the killing, the accused and the man fled the flat.

The court then heard how, back at the flat, he was on a sofa making a “spliff” while the older man was on another sofa where two knives were next to him.

Koy, he said, was sitting in a swivel chair.

He said he suddenly heard the older man ask Koy “What happened to that pack I gave you?”

The boy told the jury “I was puzzled by what he meant. I had never seen him give Koy a pack of anything.”

He said before Koy could reply the intercom buzzer sounded indicating someone was coming up to the flat to buy drugs. He said the older man got up to let two women into the flat who had bottles of aftershave with them which they exchanged for crack cocaine and heroin.

The accused said the man allowed them to go into a bedroom to take the drugs before standing in front of Koy in the swivel chair and asking again “What happened to that pack bro?'

“Koy said that he lost it,” the teenager told the court.

The older man, he said, then asked the 15 year old “What do you mean you have lost a pack?”

Continuing his evidence he said he didn’t think it looked serious, but he said the older man began saying to the boy “Why are you not speaking?”

He said he couldn't see Koy because the older man was standing in front of him.

“That’s when he (the older man) stepped back to where he was sitting and grabbed the white knife.”

The defendant said he thought the man was going to threaten Koy with it to make him speak and again he said to the youngster “Why are you not talking?”

As he said it, the man was pointing the blade at Koy, he said.

“I didn’t think nothing of it - I thought it was a bit intimidating. That's when he stabbed him. Koy wasn’t speaking - I think he was in shock. It was twice, but it was quick. It wasn’t hard, hard force, but there was force with it.

“I froze, I literally froze.”

The defendant has pleaded guilty along with the 22 year old man to a charge that they conspired together and with Koy to supply a controlled drug of Class A.

The man 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.

The trial continues.