The 38-year-old man died after being struck once in the chest at close range at the home in Cliveden Avenue, Oxley in the early hours of Tuesday morning.
Detective Superintendent Andrew Massingham says four men and a woman armed with a 12-gauge shotgun, and potentially a handgun, were involved in the attack.
"The male deceased was struck at very close range, and we believe the weapon involved was a 12-gauge shotgun," he told reporters on Tuesday.
Det Supt Massingham said the man had been sitting in a car near the home when the five turned up and started assaulting another man who lived at the home.
The 38-year-old then got out of his car and started running to the man's aid when he was shot.
The second man has suffered minor injuries and is being questioned.
Police are probing a dispute between the two men and the five suspects one to two weeks before the shooting.
"Certainly there was significant conflict amongst the whole group," Det Supt Massingham said.
The dispute was not related to number of recent gang shootings in the city's south, he said.
The attack lasted about 30 to 40 seconds and neighbours heard more than one shot being fired.
Detectives are still hunting for the five, and are reviewing CCTV footage of a car leaving the scene, which is across the road from a primary school.
Police released an image of the car in question late on Tuesday afternoon.
Det Supt Massingham urged anyone with information about the attack or the whereabouts of the alleged culprits to contact police.
"We have a number of persons with significant weaponry and it's important that we harness what information is available in the community this morning to set us on the right track," he said.
The shooting occurred across the road from the Corinda State School less than six hours before hundreds of students were due to return to class after school holidays.
There's also a preschool and a childcare centre on that block in the quiet, mainly residential suburb.
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