The man who landed a fatal punch on Sydney teenager Daniel Christie has been found not guilty of murder, but guilty of manslaughter.

Shaun McNeil was arrested on New Year's Eve 2013, shortly after his attack on the 18-year-old who was out celebrating with his brother.

A police video, which was shown to the court and released after the verdict, shows McNeil telling a police officer a "scuffle" broke out after a conversation with a group of people in the street.

The jury was told McNeil, 27, had got into a fight with a separate group of three teenagers who had tried to sell him the drug ecstasy a short time earlier.

Shaun McNeil has been found guilty of manslaughter, but cleared of murder, over the one-punch death of Daniel Christie in Kings Cross. ( ABC TV )

McNeil punched one of the teenagers and then kicked him while he was on the ground.

Another member of the group then retreated towards Mr Christie and his brother, and said they had been attacked.

"This dude has just hit all of us," the youth told Mr Christie.

Mr Christie was heard to say: "What's going on? What are you hitting a kid for?"

McNeil then said: "I'm an MMA fighter."

He then punched Mr Christie, who fell backwards.

His head hit the road below and he later died in hospital.

In an interview with police after his arrest, McNeil said: "One hit and I'm in this situation now."

Police told him that Mr Christie, who was still alive in hospital at the time, was not part of the other group of teenagers.

McNeil said: "If that has happened, I'm 100 per cent apologetic."

Prosecutors accused McNeil of giving police a false version of what happened when he suggested three people were coming at him.

Sorry, this video has expired Shaun McNeil speaks to police after the assault

But McNeil's barrister said his client did not intend to cause serious bodily injury when he punched Mr Christie.

McNeil bowed his head in the dock after the verdict was read out.

Earlier in the trial, McNeil pleaded guilty to manslaughter but not guilty to murder.

Victims of Crime Assistance League vice-president Howard Brown said it was disappointing McNeil was not convicted of murder.

"There was no real doubt that this person intended to inflict grievous bodily harm, which is all you need to establish, to secure a guilty plea of murder," he said.

"So for the jury not to have come back with that decision, it's not only disappointing for the family obviously of the young deceased, but also for the community, because the community has to have some confidence in the administration of justice."

McNeil will face a sentencing hearing in August.