Officers were called to Cleeve Close in Mt Druitt, western Sydney, about 9pm on Friday with reports of an assault.
They found a man in his 30s stabbed in the torso and rendered assistance before paramedics arrived.
The man died at the scene, despite their best efforts, prompting police to issue a public appeal for assistance on Saturday.
CCTV vision, published by media outlets, showed a group of several men walking along a street before a man threw a punch and was chased and attacked by three others in retaliation.
Blacktown commander Superintendent Brendan Gorman told reporters detectives were open to several possibilities and looking for "about a dozen people in the area at the time" to assist.
A number of items were seized at the scene, with the attack described as having been carried out with a bladed weapon.
Officers needed to wait for a post-mortem examination to be certain of which kind, Supt Gorman said.
The circumstances of the initial interaction were unknown and it was still to be determined whether the slaying was random or targeted.
"At this stage, I would say it's a horrendous incident and it's certainly concerning for police," he said.
The deceased - yet to be formally identified - was believed to have "some history" with police, and possible gangland links are one of detectives' many lines of inquiry.
Video footage from numerous sources will help officers patch together the murky train of events.
"Police have seized a number of videos from CCTV and also mobile phone videos that have been circulated," Supt Gorman said.
He requested assistance from the public, including vision or information, for their investigation.
NSW Police on Saturday also appealed for help in solving a stabbing death at North Albury, on the Victorian border.
A 28-year-old man was stabbed to the neck about 1am on September 27 before he died in hospital after a week of treatment last Sunday.
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