Haunting words in fatal NSW one-punch case

"Every day I wish I could go back to that night and just keep walking."

Nicholas Lambaditis penned those words in a letter to the parents of the Brazilian man he fatally punched in 2013, his sentencing hearing heard in Sydney on Friday.

The words "keep walking" haunt many people in the case that has left a mother and father mourning their son Lucio Stein Rodrigues, and a Sydney man with no history of violence guilty of manslaughter.

Lambaditis experienced a moment of "uncharacteristic madness" on November 3, 2013, while out for a bucks night in Sydney's CBD.

The 34-year-old, who appeared in the NSW Supreme Court on Friday, was "annoyed" after being refused entry into the Scruffy Murphy's Hotel in the early hours.

As he was walking away he came across 34-year-old Brazilian biologist, Mr Rodrigues, and his friend Eric Heward.

The hearing was told Lambaditis heard words to the effect of "keep walking", which he believed came from Mr Heward.

Lambaditis, who has pleaded guilty to manslaughter, said something to Mr Heward before he assaulted him, sparking Mr Rodrigues to intervene.

Lambaditis hit Mr Rodrigues, knocking him to the ground, leaving him with an injury that killed him.

Crown prosecutor Trevor Bailey told the court whether or not Mr Heward said the words "keep walking", Lambaditis's response was disproportionate.

Mr Rodrigues's family, many of whom travelled from Brazil, dabbed their eyes as statements detailing their pain were read out in court.

"It is our hope that every time the accused looks at his hands he remembers that they took Lucio's life," parents Lidia Pagotto Stein Alves Rodrigues and Rogerio Roberto Alves Rodrigues wrote in a statement.

"When holding a flower, when touching or hugging somebody, when making a toast in celebration of something, when holding a child...

"May he remember the result of his actions and that on the other side of the world a family is incomplete and cries for the loss of a loved one."

Mr Heward, who was with Mr Rodrigues in his final moments, said the event would haunt him for the rest of his life.

"I have missed a lot of work because I have been quite anxious and depressed," his statement read.

Taking the witness stand as his mother watched from the public gallery, Lambaditis labelled his actions that night "reckless and beyond measure".

His barrister Ertunc Ozen described the attack as one moment of "completely uncharacteristic madness".

Lambaditis will be sentenced on June 12.