The father of a 16-year-old boy who was stabbed to death by another teenager on the Sunshine Coast has detailed to a court the moment he saw his "motionless" son take his final "incredibly deep gasping breath".
Balin Stewart died shortly after being wounded in the chest by a 17-year-old boy outside his Buddina home in January last year.
On Monday, the now 18-year-old, who cannot be identified, pleaded not guilty to murder at the beginning of a 10-day trial in Brisbane.
Crown Prosecutor Rebecca Marks told a Supreme Court jury there had been years of hostility between the two boys which stemmed from their association with a teenage girl.
"[The defendant] didn't like Balin," she said.
Ms Marks told the jury it was not contested the defendant used a 12cm knife to penetrate Balin in the heart during a fight, but they would need to determine his intention when he did so.
"The issue will really centre around whether you consider … at that time he intended to kill him," he said.
The teenage girl, who also cannot be named, witnessed the stabbing and her interviews with police were played to the jury.
In her initial interview, the upset teenager told the investigator she had been with Balin at his house, when the pair sent the defendant a recording of them cuddling "to provoke him".
"We just wanted to send a video to [the defendant] and be like 'haha'," she said.
The girl said the defendant allegedly replied "does Balin want to fight?" before sending another message, saying "come out".
She explained she and Balin went outside and saw the defendant was there, and the two boys began fighting.
The girl said she managed to separate them, and it was at this point the defendant allegedly told her "I'm [going to] f***ing kill him", and then the boys started wrestling again.
She described seeing the defendant hit Balin from the side but was not aware he was stabbed until she saw him with blood on the ground.
The jury heard Balin's parents were home at the time and came rushing outside to try and help their son.
Kerri-Lyn Stewart took the witness stand first and told the jury she woke to the screaming teenage girl banging on her bedroom window.
"At the time I didn't know if it was excitement or distress because it was very high pitched," she said.
"Then I heard her say hurry up [the defendant] stabbed Balin."
'I'm sorry I can't believe I did it'
Once outside, Mrs Stewart told the jury she saw her son unconscious on the ground, and the defendant holding his phone, and she told him to call triple-0.
"He was saying 'I'm sorry, I'm sorry I can't believe I did it'," she said.
"He was quite distressed."
Balin's father Michael Stewart told the court, when he came outside, he first saw his wife with their "motionless" son, but then turned his attention to the defendant.
"I really don't know what I was going to do ... I wasn't calm I guess," he said.
"He started saying don't hurt me, don't hurt me, I'm sorry."
Mr Stewart told the jury his wife called him back to help their son, but efforts to resuscitate him were unsuccessful.
"He took an incredibly deep gasping breath and went silent," he said.
Ms Marks told the jury other witnesses will testify the defendant allegedly spoke of wanting to kill Balin before that night, and after the stabbing he told a friend he "regretted it".
"He said ... he was really jealous and got so angry that he wasn't thinking and just grabbed [the knife]," she said.
The trial before Justice Elizabeth Wilson continues.
