A 13-year-old charged with murder following the fatal stabbing of a father in Sydney's west last week was known to police, in a case investigators have described as "absolutely senseless".
About 8:25pm on Friday, emergency services were called to Cleeve Close in Mount Druitt near the Westfield shopping centre and train station, where they found a 36-year-old man suffering stab wounds to his torso.
Despite efforts to render first aid, the man died from his injuries at the scene.
Police said a 13-year-old male was arrested at Mount Druitt Police Station on Sunday.
The stabbing occurred near the Westfield and train station on Friday night. (ABC News)
He was charged with murder, breach of bail and an unrelated offence of robbery in company.
That same day, police attended a home in Cabramatta in Sydney's south-west where they arrested a 16-year-old male.
He was taken to Cabramatta Police Station where he was charged with accessory after the fact to murder.
The teenagers were refused bail to appear before a children's court on Monday.
'Chance meeting that was totally innocent'
On Monday, Superintendent Darrin Batchelor, from the Mount Druitt Police Area Command, said the 13-year-old, who cannot be legally identified, was known to police.
He described the fatal stabbing as "absolutely senseless".
"In my 30-year career in policing, I find this absolutely senseless … he was going about his business, stopped to talk to some family friends who is now dead."
Police will allege the 13-year-old stabbed the victim twice.
Superintendent Batchelor said about a dozen young people were in the vicinity of the incident on Friday night when an altercation ensued with the 36-year-old male.
"That altercation seems to be a chance meeting that was totally innocent," he said.
"The 36-year-old was on his way home. He is employed from the local area, and was speaking to a number of young people that he knew through family and friends, and another group of young people took offence to that conversation that the 36-year-old male was having with those young people, and as a result of that … that 36-year-old male is now [allegedly] murdered."
Superintendent Darrin Batchelor says it appears the altercation stems from a chance meeting. (ABC News)
Before being stabbed, the man had been planning to help some of his young family friends at the scene get home safely.
"He was doing a good deed. He went to an ATM to withdraw money so that those [young] people could get home safely," Superintendent Batchelor said.
Police are expected to carry out further arrests and charges after seizing multiple mobile phone videos and CCTV footage of the incident.
Family left distraught
The deceased was described as a family man with children, with his loved ones "obviously distraught" by his death.
"A family has lost a father, a son, a brother," Superintendent Batchelor said.
Though forensic testing is still to occur, investigators believe they recovered the weapon used in the incident, a knife, from a drain outside a Cabramatta unit block.
Over the weekend, a nearby worker recounted hearing screaming on Friday night and saw children running from the scene.
Another local called emergency services at the time when he saw the man on the ground.
"Everyone was helping [him] … it scared a lot of people," he said.
NSW Premier Chris Minns told 702 ABC Sydney on Monday that while he would not comment on the specific case, he was worried about the rise in younger cohorts of people committing violence crimes.
"That is a particularly heinous and morally objectionable," he said.
"We need to make sure that we've got policies in place to meet that threat where it's most acute."