Instead Nathan John Caulfield, Trent Edward Dyhrberg and Kalabe John Steven Saurine arrived at Donney's rural property north of Brisbane, a jury heard.
Caulfield had a sawn-off rifle and Saurine was armed with a machete, Brisbane Supreme Court was told on Monday.
Minutes later Caulfield allegedly shot Mr Zanco in the head, crown prosecutor Michael Lehane said.
Mr Zanco died the next day after Caulfield transported the 22-year-old to hospital in the back of his ute before fleeing, court was told.
Saurine later told police Caulfield, Dyhrberg and himself had planned to rob Donney of his drugs and or money, Mr Lehane said.
But instead of alleged drug dealer Donney, the trio found Mr Zanco having takeaway on the couch with friends when they arrived at the Amamoor property near Gympie in the early evening in March 2020.
Mr Zanco had only been living with Donney for about two weeks while helping out on the property.
Caulfield was one of the few people who had a problem with Mr Zanco and he also had a grievance with Donney, Mr Lehane said.
Mr Zanco was left alone on the couch when the trio entered the house, with Dyhrberg holding the front door shut, the court heard.
"Three against one. No Donney, just Michael Zanco but he'll have to do," Mr Lehane told the jury.
"Within a few minutes, possibly even less, Caulfield shoots Michael Zanco in the head.
"Once the bullet went into his head, Michael Zanco never stood a chance - he dies the next day."
Saurine allegedly wrote a letter intercepted by Corrective Services that said Caulfield had "shot old mate in the head point blank".
"It was crazy bro and now I'm getting charged with armed robbery and murder," it said.
Mr Lehane said when Caulfield shot Mr Zanco he intended to kill him or cause grievous bodily harm.
"Or if he didn't have that intent he was part of an unlawful plan to rob and or assault which involved the use of weapons including the gun," he told the jury.
"The use of that gun clearly included acts which were likely to endanger human life."
Mr Lehane said Saurine and Dyhrberg were part of the plan.
"They knew about the gun and it was a probable consequence ... that Michael Zanco would be killed," he told the jury.
"The crown case is ... they should quite rightly bear criminal responsibility for this young man's death, just as Caulfield should."
Caulfield, Dyhrberg - both 36 - and Saurine, 22, on Monday pleaded not guilty to murder at the trial before Justice Peter Davis.
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