A jubilant Joshua Lindsay Elkerton-Sandy, 21, was embraced by supporters when he walked free late on Wednesday after being acquitted by a Brisbane Supreme Court jury.
Earlier, some of the same supporters had physically clashed with a group aligned with Kane Alexanderson, who was 18 when he died of a stab wound to the heart three years ago.
After the verdict, tensions boiled over between the two groups outside the court building despite a heavy security presence as Elkerton-Sandy supporters waited for the 21-year-old to emerge.
Fights broke out before Elkerton-Sandy supporters retreated back into the courthouse, sprinting to evade a rival group in pursuit.
A woman was restrained by a number of security in the court foyer.
Police soon arrived with a number of officers standing outside the court building.
A smiling Elkerton-Sandy emerged hours later from the courthouse with the rival group no longer in sight, receiving a kiss on the head from a supporter.
The jury heard Elkerton-Sandy reached for a knife when a group including Mr Alexanderson barged into a Brisbane CBD high-rise apartment three years ago.
Members of the group had a "beef" with Elkerton-Sandy and planned an attack for days, defence barrister Stephen Kissick told the jury.
A nine-strong group including Mr Alexanderson had been drinking at a building nearby and left to confront Elkerton-Sandy who was at the apartment with friends to watch Australia Day fireworks.
The group snatched a security card for the apartment and seven members were able to barge their way in with Mr Alexanderson leading the charge, the court heard.
Some were armed with beer bottles.
After a confrontation that lasted barely a minute, the group fled with three members suffering stab wounds.
One was slashed in the face, another in the torso and arm while Mr Alexanderson was stabbed twice, including a 6cm-deep wound that penetrated his heart.
He died six days later.
"There will be no ... contest that Joshua Elkerton-Sandy caused Kane Alexanderson's death," crown prosecutor David Nardone had told the jury.
"The question becomes did Joshua Elkerton-Sandy lawfully act in self-defence?"
Mr Kissick told the jury that Mr Alexanderson was part of an intoxicated mob who had committed a violent home invasion.
He said Elkerton-Sandy had reached for the first thing that he could see when the group entered and grabbed a knife.
"If seven people ran into your house unexpectedly, what would you do?" Mr Kissick asked the jury.
"He chose to stand up to this gang ... he was obviously entitled to defend himself."
Elkerton-Sandy told police that he had a falling out with some of the group's members because he no longer wanted anything to do with their lifestyle, the court heard.
He said once the group burst into the 17th floor apartment, they punched and kicked him, smashing bottles over his head.
Elkerton-Sandy claimed he was pinned against the balcony and "half hanging over" before his girlfriend grabbed him, the court heard.
"Why am I getting in trouble ... I am the victim," he told police.
After Justice Sean Cooper warned the packed public gallery that they could not express their feelings about a verdict, Elkerton-Sandy looked up in relief when "not guilty" was read out by the jury.
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