A man convicted of the 1995 manslaughter of a Sydney schoolboy has told a jury he kicked the victim without realising he had been stabbed.

He said his friend, Abraham Rodriguez, later showed him a folding knife which had a red substance on it and said, "I think I stabbed him, I stabbed him".

The witness, who cannot be named as he was 17 at the time of the crime, was giving evidence on Wednesday at the trial of his friend's father, Rafael Rodriguez.

The 60-year-old has pleaded not guilty in the NSW Supreme Court to being an accessory after the fact to murder.

Crown prosecutor Margaret Cunneen SC alleges he disposed of the knife and helped his then 18-year-old son flee to El Salvador, knowing he'd murdered Peter Savage.

The 16-year-old schoolboy was fatally stabbed on August 24, 1995, at Lidcombe in Sydney's west, as he walked home from rugby training.

Ms Cunneen said the jury would have to be satisfied that he was murdered by Abraham Rodriguez and that his father, knowing he had committed the crime, assisted him.

The father's barrister, Peter Hamill SC, disputes that the stabbing would amount to murder, that the son committed the homicide and that the father disposed of the knife.

The witness had been charged with murdering the schoolboy but was instead convicted last year of manslaughter and robbery in company, he told the jury on Wednesday.

He received a 15 per cent discount on his sentence for undertaking to testify against Rafael Rodriguez and, if he ever went on trial, against his son, who has not returned from El Salvador.

The witness said he was with Abraham Rodriguez at Lidcombe on the night of the attack when he went into a phone booth to ring his girlfriend.

"Then I heard a scream, a male, from behind me," he said.

He said he could see his friend further up the road and then saw "a boy in a school uniform sitting on the ground" in the middle of the road.

He did not notice any injury on the boy and said to him, "Why did you hurt my friend?"

"When I heard the scream, I believed it was Abraham, I believed he was hurt," the witness said.

The boy replied: "He's got it, he's got it."

"I just kicked him on the leg ... pretty hard," the witness said.

When he caught up with his friend, Abraham showed him the knife.

"He said the kid sprayed him in the face."

The jury has been told a can of deodorant was found at the scene.

The witness said his friend later produced a wallet, saying, "Here you go, take it".

But he said he refused and Abraham Rodriguez put the wallet in an industrial bin.

He agreed he had a criminal history of violence.

The trial is continuing before Justice Peter Hidden.