A young man high on the drug ice fatally shot his childhood friend in broad daylight because he feared for his life, a court has heard.

Graham Smith, 22, sobbed in the NSW Supreme Court as the mother of the man he allegedly shot, painfully recounted the moment she found out her son had been killed.

Smith is accused of shooting Joshua George in Claymore in Sydney’s southwest last January after a drug-fuelled argument.

Smith, who has pleaded not guilty to murder and is on trial, and Mr George had spent the night together at friends’ houses on January 19 and the early hours of January 20.

Both had used ice and prescription drugs, the court heard.

Mr George’s mother, Gemma George, could only manage one-word answers through her tears as she gave evidence on Monday.

She confirmed Smith and her son had always known each other but only started to spend a lot of time together in the months leading up to the shooting.

Smith’s defence barrister Kate Traill said the young men shared a common interest.

“It was the drug ice,” she said.

The court heard Mr George was waiting to be admitted to a rehab facility to battle his drug use when he died.

The morning before Mr George was shot, Smith had allegedly called Mr George’s friend a dog and believed he had passed on fake drugs.

Crown prosecutor Michael Barr said a confrontation between Mr George and Smith, 24, broke out on the street and Smith hit his mate with a bicycle fork.

Mr Barr said witnesses would give evidence Mr George was walking towards Smith’s house, after claiming a one-on-one fight had been organised, when he was shot.

The court heard Smith had been behind a fence and a friend had tried to get the rifle off him.

The bullet went through Mr George’s lung and doctors located it in the back of his chest.

He died in Campbelltown Hospital that afternoon.

Smith has argued he acted in self-defence when he fired the gun because he feared for his life.

Ms Traill said Smith thought Mr George had a gun.

“He shot him to defend himself and he shot him because he feared for his life,” she told the court.

The trial continues.