The knife used to fatally stab a 15-year-old Watford boy belonged to his mother, a jury heard today.

The white knife had been found by Sharon Bentley in her son Koy's bedroom two weeks before he was attacked in a drug den in the town.

In a statement read to the jury, Ms Bentley said the knife was shown to her by the police following her son's death.

She said: "This knife belongs to me and is from a set of knives I bought. It is the same knife I found in his bedroom 2 weeks before his death. He said he had found it under his bed. I put it back downstairs in the knife drawer."

Pathologist Dr Charlotte Randall, in a report read to St Albans crown court, said that having examined the injuries to Koy she thought it was likely that they had been caused by the white knife.

A 16-year-old North London boy - who cannot be named for legal reasons - is accused of murdering Koy, who was stabbed twice in the chest.

The fatal wound passed through Koy's ribs into his chest cavity, through the lower left lung and into his heart.

The alleged killer, from North London, and a 21-year-old man who was with him, fled from the flat in Rainbow House, Water Lane.

In her statement, Koy's mother Sharon said she had separated from his father Owen when their son was a year to 18 months old. She said: "He got into a few problems with problem lads in Watford and we sent him to live in Bournemouth with his aunt. Then he came back and lived with his father.

"He was arrested for carrying a Rambo knife, which he told me he found in a graveyard."

Ms Bentley said Koy then came back to live with her and did school work from home. He was getting help from Youthpoint and Gatehouse, an organisation linked to social services.

She said: "During the week before his death, he changed. He started going out at around 11am. He would not tell me where he was going. I thought he might be seeing a girl."

Earlier Prosecutor William Harbage QC told the jury of five men and seven women that Koy, the accused and the 21-year-old man were all involved in supplying Class A drugs from the flat in Rainbow House.

On the afternoon of 5 June, two women who had bought drugs earlier returned to buy some more. To fund their purchases they had been shoplifting in Watford town centre and arrived at the flat to exchange stolen aftershave for drugs.

The women went into the bedroom to take the drugs leaving the teenage boys and the 21-year-old in the open plan kitchen-dining area.

Giving evidence last week, the older man said they were selling wraps of crack cocaine and heroin for £10 a time. At first they would give wraps away for free as a way of encouraging buyers to come to them.

He said they all got on, but on one occasion her heard banter between the two of them in which they were saying to each other: "I will stab you, I will stab you."

On the day of the killing he said they were in a good mood, but he noticed the defendant was holding Koy by the neck.

"Koy was saying: 'Don't hold me like that, no one holds me like that.'"

He said he told them to stop messing about and looked down. He told the jury he heard a thud which he though was a punch.

Asked about the accused, the man said: "He had a knife in his right hand. It was a stainless steel knife. It had blood on it.... on the tip of the blade. His arms were by his side."

He said Koy stood up from a swivel chair and pulled his jumper up. "I could see blood pouring out from under his left armpit."

The defendant, he said, was apologising to Koy.

The man said he and the accused were panicking and told him to apply pressure to the point where the blood was coming from.

He said he ran into the bathroom and hid the drugs in “backside” and then told the women to call an ambulance and to say that Koy had fallen onto a knife. The teenager ran out of the flat and he left moments later.

The teenager denies murdering Koy, who lived in Watford, on June 5 last year. He and the older man, who is now 22, have pleaded guilty to conspiring with Koy to supply Class A drugs.

The 22-year-old has also pleaded guilty to perverting the course of justice by instructing a woman who was at the flat that afternoon to lie to the ambulance crew about how Koy received his injuries. He also told another woman she should return to the flat and remove any incriminating evidence.

Koy's father Owen Witter said, also in a statement read to the jury today, that it came as a shock when Koy was arrested for carrying a knife on 25 July 2016. He said: "He had been robbed in the past and it may have been something to do with that. He did not appear frightened or in fear of anything."

He said that the last message he sent him was three days before he died. He said had bought him new jeans and a jacket and had sent him a joke message of Jeremy Corbyn rapping.