Despite the teenager's intoxication and his bizarre behaviour, Justice Michael David concluded that he had the necessary intent to kill.
The judge, who heard the trial without a jury, found the now 18-year-old guilty of the murder of Lewis McPherson, 18, and the attempted murder of Liam John Trewartha and James Peter Lamont on December 31, 2012.
Relatives and friends of the dead teenager shed tears of relief on Friday as the Supreme Court judge rejected the defence contention that he was so drunk he could not form the intent to kill.
"I have put aside understandably subjective feelings such as the loss of an innocent young man's life," the judge said.
"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 was every chance that as many as four people could have been killed on that evening."
Mr Lamont testified that as the trio walked to the party, they came across the teenager, an acquaintance, who was bare-chested and carrying a silver pistol.
After they greeted him, the teenager's only response was: "f*****g c***s" before he fired four shots at them and ran away.
One witness said the shooter returned to the scene and pointed the pistol at the abdomen of the dying victim saying: "If you don't stop being dead, I am going to make you really dead".
The judge found that the teenager was involved in a fight at another party and was angry when he left it while holding the gun.
After cocking, pointing and firing it at the three friends, the teenager fired at an oncoming vehicle.
While accepting he had been grossly intoxicated, the judge said he had the presence of mind to flee from police and to try to hide the weapon, and was able to give coherent answers about his age and other details.