Mr Singh (30), a father of three, died in hospital after being shot in the chest with a .22 rifle during an armed robbery at his Manurewa liquor store on Saturday night.
As Mr Singh fell to the floor, the gunman and his two accomplices rifled through the store's stock, taking boxes of alcohol and the contents of the till.
Security camera footage shows them laughing as they leave.
Police and ambulance officers were called to the scene by Mr Singh's colleague within minutes of the shooting, but it was another half an hour before paramedics were allowed into the scene.
Mr Singh's grieving family believe that delay hindered the 30-year-old's chance of survival, and they want answers.
Manurewa MP George Hawkins has also raised concerns about the delay, and plans to meet acting Police Commissioner Rob Pope today.
However, police and ambulance officers have defended the time it took them to enter the liquor store, saying it was an armed situation and best practice procedures - which included waiting at a safe point - had to be followed.
Detective Inspector Jim Gallagher said police had to establish the gunman's whereabouts to ensure no-one else's life was put at risk.
They also had to wait for firearms so armed police could check the scene before letting anyone, including ambulance officers, into the store.
However, family friend Sandeep Verma - who arrived minutes after the shooting - said he told 111 operators the armed robbers were long gone so there was no excuse for not letting help in sooner.
"This is not acceptable. Everyone was calling cops and an ambulance from the car park so that means no-one is around," Mr Verma said.
"If you are still waiting for police, then that means they are just abiding by the rules - they are not human beings. They just follow the rules which are on the books, that's it."
While waiting for help, Mr Singh made his way to the toilet before returning to the floor, where he vomited blood several times.
He was unable to lie still for long due to the growing pain and kept asking his wife - who had been called to the scene by the co-owner - to call for help.
Mr Verma made several calls to 111 as his injured friend's condition deteriorated, but despite being able to hear the sirens down the road, help did not come as promised.
"I said to them `he's vomiting blood' . . . they said the ambulance is just one minute away," said Mr Verma.
"I was pretty much assured the ambulance was just around the corner but they didn't arrive."
When asked if having an ambulance there sooner would have saved Mr Singh's life Mr Verma replied: "Yeah, sure."
"If ambulance would have come in 10 to 15 minutes then I think there was chances of his survival."
Mr Gallagher said there would be a review into the response time but he maintained police did their best given they had to follow procedures.
St John Northern Regional operations manager Gary Salmon said waiting at the safe point was difficult for paramedics, but it was absolutely vital given the dangers involved in responding to a shooting.
"This is one of the worst situations our crews can be in. They are surrounded by potential danger, they have a patient which is known to have been shot . . . and yet we can't get to them.
"We are terribly sorry for the feelings of the family and we understand entirely how they must feel knowing that we are so close and yet not there, but the problem for us is we have to know the zone is safe."
Mr Salmon said it was difficult to say what would have happened if paramedics had reached Mr Singh sooner.
"All I can say is we had a very highly qualified and experienced crew with the patient as soon as we possibly could."
Mr Salmon planned to visit Mr Singh's family last night to explain why and offer his condolences.
