A 16-year-old boy was seen smirking after using a “metre-long” sword to kill another teenager at a flat being used by drug dealers, a jury has heard.

The youth, who cannot be named because of his age, denies the murder of 17-year-old Nasir Patrice and is expected to argue that he was acting in self-defence, Warwick Crown Court was told.

Opening the Crown’s case against the defendant, who is from London, prosecutor Michael Burrows QC said the youth is alleged to have taken a taxi to a guest house after the killing, where he pulled out a “nasty-looking blade” and claimed to have “dropped” two people.

The youth, now aged 17, also denies attempting to murder another victim who suffered a collapsed lung and spent five days in hospital.

Giving the jury panel what he described as an overall picture of the events on the morning of January 15 last year, Mr Burrows said Nasir was stabbed after he and two friends were seen entering a flat in Tachbrook Road, Leamington Spa.

Mr Burrows said of the youth accused of murder, who was staying at the flat: “He was armed with a large knife, a sword, which he used to kill Nasir Patrice.

“The prosecution say he murdered him and intended to kill. I understand it is his case that he acted in self-defence.”

Telling jurors that Nasir suffered four stab wounds, Mr Burrows added: “There is, of course, a background to this case – that background is drugs.”

Evidence will be put before the court that the youth accused of murder and Nasir were “rival dealers”, Mr Burrows said.

The court heard that another man staying at the flat had been leaving the property to fetch cigarette papers for the youth accused of murder when three men “rushed” inside.

Mr Burrows said of the witness: “He was confronted by three males who had burst into the flat.

“He heard shouting and screaming. He heard someone shouting ‘Put it down, put it down.’

“You may conclude that that was one of the three men who had gone past him to get into the flat.”

Jurors heard that the witness stopped to get his breath back, and the same three men came out of the flat within a minute or so.

“They were screaming for help,” Mr Burrows said. “He (the witness) didn’t see any weapons at any stage – either when they went into the flat or when they came out.”

Jurors also heard claims that the defendant emerged from the flat “30 seconds or so later” and “looked around and smirked” before leaving.

Nasir, from Birmingham, was pronounced dead nearby despite the best efforts of medical staff.

An air ambulance was called to the scene and arrived at 11.10am, but Nasir was declared dead at 11.23am.

Mr Burrows continued: “One of the stab wounds to the chest went through the body.

“The pathologist considers that that would have required what he describes as the upper tier of force.”

The defendant, who also denies perverting the course of justice, is alleged to have asked two builders to call him a taxi before leaving the area.

The trial continues.