THE teenager who shot and killed Lewis McPherson on New Year's Eve has been found guilty of murder - and of attempting to kill his best friends.

The Supreme Court gallery, packed to overflowing with Mr McPherson's family and friends, was reduced to tears of relief and hushed cheers as Justice Michael David this morning handed down his verdict.

The teenager was also found guilty of attempting to murder Mr McPherson's two best friends - James Lamont and Liam Trewartha - in the same incident.

In his published reasons, Justice David said he had "clinically and objectively assessed" all the evidence placed before him during the teen's trial earlier this month.

"I have put aside understandably subjective feelings such as the loss of an innocent young man's life," he wrote.

"I have set aside my feelings of indignation and horror that a young man, affected by drugs and alcohol, had access to a loaded weapon which he has openly taken onto a public street and discharged four or five times.

"There is every chance that as many as four people could have been killed on that evening."

He also noted expert evidence suggested the killer teenager was grossly intoxicated when he fired four shots at the trio.

"Although his condition was one of gross intoxication and his behaviour was in many ways bizarre, nevertheless I find it proved beyond reasonable doubt that the accused had the intention to kill," he wrote.

Justice David now faces the difficult task of sentencing the teen, who must be dealt with under the provisions of the Young Offenders Act (1993).

Though his crime attracts an automatic life sentence, his non-parole period must encourage rehabilitation and a successful return to the community due to his age.

Non-parole periods handed down under the Act vary greatly.

In 2010, the teenager who stabbed and killed schoolboy Daniel Awak in broad daylight on Grenfell St, Adelaide, received a six-year non-parole period.

Last year, two 18-year-olds who murdered pensioner Anne Redman received 20-year minimum prison terms.

The teenager, who cannot be identified, stood trial in the Supreme Court this month before Justice David, who sat in the absence of a jury.

He pleaded not guilty to murdering Mr McPherson, and further denied attempting to murder Mr Lamont and Mr Trewartha.

At trial, prosecutors alleged he fired four shots at Mr McPherson, Mr Lamont and Mr Trewartha on Sixth Avenue, Warradale, in December 2012.

They further alleged that, after shooting Mr McPherson, the teen stood over him with the gun and said "if you don't stop being dead, I'll make you really dead".

Prior to the shooting, the teen had attended a New Year's Eve party with his friends at which a fight broke out over the sale of the drug known as ecstasy.

Attendees of that party gave evidence one of the accused's friends demanded he bring his .22 calibre handgun into the dispute and, when the teen refused, they argued violently.

They said the teen was visibly emotional and distressed after the incident, and left the house carrying the gun.

At that time, Mr McPherson, Mr Lamont and Mr Trewartha were walking past the house on their way to a different New Year's Eve party.

In their evidence, Mr Lamont and Mr Trewartha said they had greeted the teen upon crossing his path, only for him to say "f - king c - ts" and open fire.

They recalled trying to keep their "best mate to the end" alive after he was shot in the chest, and fleeing in terror when the alleged killer returned.

Prosecutors alleged the teen then stood over the dying Mr McPherson and told him "if you don't stop being dead, I'll make you really dead".

The court also heard expert testimony that the teen's blood alcohol at the time of the shooting was between 0.252 and 0.284, and showed traces of ecstasy and cannabis.

The teen opted not to take the stand and give evidence on his own behalf.

His lawyers argued he was too intoxicated to have formed the deliberate intent to hurt anyone, and therefore could not be guilty of murder and attempted murder.

They presented their own expert evidence which suggested the teen's alcohol and drug consumption would have left him impulsive, aggressive and paranoid.

In his written reasons for verdict, Justice David the prosecution had proven its case beyond reasonable doubt.

However, he said the teen's alleged final words to Mr McPherson remained contentious.

"I find that the accused returned in anger and pressed the gun into the deceased's chest while he was still alive," he said.

"I give the accused the benefit of the doubt as to whether he said the words attributed to him.

"If he did say those words, they could not assist the accused's defence despite their bizarre nature."

He remanded the teen in custody to a pre-sentence hearing next month.

Outside court, members of the McPherson, Lamont and Trewartha families wept, embraced and expressed gratitude that their long ordeal was coming to an end.

Mr McPherson's father, Mark, said he was "very pleased" with the verdict.

"I think it's the only verdict that would have been right," he said.

"This whole case underlines some of the issues we are facing in society - alcohol-fuelled violence, guns and drugs.

"As a community and as parents, we need to deal with these things along with our children."

He thanked his family, friends, prosecutors, SA Police and the public for their support.

"(The verdict) doesn't really help, I suppose - nothing will change what's happened - but it gives us some feeling of justice," he said.

"There's a lot of people hurting and there's another family (the killer's family) hurting as well ... we feel for them."

Mr Trewartha's father, Alan, said justice "had been done".

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