In its ruling, the Court of Appeal said it was satisfied the trial judge had properly instructed the jury after a "difficult and lengthy" hearing.
"His charge was well structured, and equipped the jury to grapple with the evidentiary and legal issues presented," the Appeal Court ruled.
The case arose in April 2006, when eight members of the Toronto Bandidos motorcycle gang were shot execution style on a farm property, the result of an internal gang dispute involving the Winnipeg and American branches. Their bodies were found stuffed in trunks of vehicles on a property near London, Ont.
The jury convicted six men of first-degree murder but only five appealed on various grounds, among them the trial judge's instructions.
At the appeal heard in September, several of the men argued they were forced to take part on the killings. One of them, Marcelo Aravena, said he feared he would "end up in a pile of dead bodies" if he didn't.
However, the trial judge ruled the defence of duress was legally unavailable.
"It is entirely irrelevant to this case," Superior Court Justice Thomas Heeney said in convicting them in October 2009. "In a nutshell, it is not open to anyone to say to an innocent victim: 'You will die so that I can live'."
The Appeal Court found that Heeney was mistaken in that conclusion. Nevertheless, it found the error caused no substantial wrong or miscarriage of justice to the men who argued they had killed under duress.
"On the evidence, there was no air of reality to that defence on any of the charges," the Appeal Court ruled.
Wayne Kellestine, on whose farm the killings occurred, argued that branding him a psychopath at trial and other character evidence was "massively prejudicial" to his case.
The other men, Brett Gardiner, Frank Mather and Dwight Mushey, were portrayed at trial as power-hungry schemers or wannabes gunning for status in the outlaw motorcycle club.
The Appeal Court, however, ruled against them all.
"This court has had the benefit of careful and thorough arguments presented on behalf of the appellants and the Crown," the court said. "We are satisfied that the appeal must be dismissed."
The men killed that night were George Jessome, 52, George Kriarakis, 28, John Muscedere, 48, Luis Raposo, 41, Frank Salerno, 43, Paul Sinopoli, 30, Jamie Flanz, 37, and Michael Trotta, 31.