TEENAGER David Paine was stabbed through the heart with a knife by a friend he was beating in a fight, a murder trial jury heard. David, 17, had punched and head-butted Christopher Ball in a row over the way the defendant treated his girlfriend, St Albans

TEENAGER David Paine was stabbed through the heart with a knife by a friend he was beating in a fight, a murder trial jury heard.

David, 17, had punched and head-butted Christopher Ball in a row over the way the defendant treated his girlfriend, St Albans Crown Court was told on Monday.

They clashed again in the early hours of the morning at Ball's house in Broad Oak Way, Stevenage.

When David got the better of the fight, Ball went to the kitchen and took a knife which he used to stab him.

Prosecutor Ann Evans told the jury that moments before the stabbing Ball was heard to say: "I am going to f...... kill you."

She told the jury: "The words and the weapon taken together can leave you in no doubt he intended to murder."

Ball, who was 17 at the time but is now 18, pleads not guilty to murdering David Paine, of Leaves Spring, Stevenage, on January 28 this year.

The prosecutor told the jury that on the night of the killing there had been a party at Ball's house for his two younger sisters. David Paine - who was a friend of both Ball and his 17-year-old brother Michael - had been invited.

But the court heard that the relationship between David and Ball was "strained". The prosecutor said that David was unhappy because he felt that Ball's girlfriend Claire was being treated badly.

Michael Ball told the jury that David and his brother had fought on the previous Boxing Day.

Then on the night of the party he said there was an argument outside on the street between Ball and Claire in which David was present. He said: "I grabbed hold of Chris and Dave hit him in his face." He said David Paine also gave him a "slight head butt".

Later, at around 5am, Michael said he and David were back at his home when Ball returned. "The two started fighting again. Dave was winning and Chris went to the kitchen," he said.

The prosecutor alleged witnesses heard Ball say: "I am going to f...... kill you." Moments later she said David Paine staggered back into the hallway with a knife protruding from his chest. "David pulled the knife from his chest. It was the last thing he did," she said.

She said a pathologist found death was due to a single stab wound to the chest with the knife having penetrated his heart and left lung to a depth of 12 to 15 centimetres.

Ball left the scene and was arrested three hours later at his girlfriend's home in Broadwater Crescent.

He asked the officers: "Is he all right?" When he was told David had died he replied: "I didn't mean to do it - he is my mate."

Miss Evans said Ball was in tears telling the police how sorry he was.

He told officers he had drunk half a bottle of vodka and had smoked three joints of cannabis.

When questioned he told the police David had gone "mad" in the living room of his home and he was "scared for his life".

The trial continues.