Friends of an 18-year-old who was shot and killed on New Year's Eve remain mystified as to why it happened.

Lewis McPherson was shot while walking to a New Year's Eve party with friends.

He, friend Liam Trewartha and another mate were allegedly confronted by a 17-year-old who had what they thought was a toy handgun.

Mr Trewartha told 7News the man came around the corner and pulled out the gun, shooting four times.

"He shot at me once, then he shot my mate, with the last shot right in his chest."

Neighbours tried CPR however had to stop when the teen allegedly returned and waved the gun at them.

Mr McPherson was rushed to hospital but couldn't be saved.

According to Detective Inspector Mark Trenwith: "There was some sort of altercation, gunshots were fired and tragically a young man is now dead."

It's believed the alleged gunman and Mr McPherson went to the same school, but according to Mr Trewartha, there wasn't any animosity between them.

"He (the alleged gunman) didn't have any beef ... I've never been on bad terms with him. I don't know what sparked it ... I wish I did," Mr Trewartha told the Adelaide Advertiser.

Assistant Police Commissioner Bryan Fahy said there didn't seem to be anything specific that sparked the shooting.

"A very short conversation took place, there was no indication that there was any argument in that conversation, which was a polite conversation, and it is alleged the offender produced a firearm and fired the shots," Mr Fahy said.

Mr Trewartha told 7News: "Just one night gone wrong, it all happened in a second. I lost a best mate."

The 17-year-old accused faced the Youth Court today over the alleged shooting murder, where his lawyer applied for a home detention bail report.