The six men are accused of the shooting in March of Uffe Larsen, a member of the rival Bandidos motorcycle gang, at the international airport in Copenhagen. Three other Bandidos were wounded in the shooting and another in an attack the same day at Oslo airport in Norway.
Until the airport shootings, most of the attacks in the gang feud had taken place at or near the bikers' rural clubhouses. But in the past eight months, attacks have increasingly been staged in heavily populated areas, raising fears that bystanders would be caught in the violence.
Those attacks have included a shooting outside the main post office in downtown Oslo and the anti-tank grenade attack last month on the Hell's Angels' Copenhagen headquarters, in which two people were killed and 17 injured.
At least nine people have died and 46 have been wounded in the three- year feud.
The murder trial is being held amid intense security. The six defendants were led into the Eastern High Court by police carrying sub-machineguns and wearing bulletproof jackets. No one with a criminal record was allowed into the courtroom and spectators, journalists and other observers were body-searched before entry.
The defendants, who cannot be named under a court order, had not seen each other since their arrests. They gave each other the characteristic bikers' hug as they met up in the courtroom. "You look great," one biker told another.
Heavily armed police officers surrounded the downtown court building while marksmen were spotted on nearby roofs. One street alongside the court was closed and parking around the courthouse will be forbidden because of fear of car bombs.
Bitte Dyrberg, for the prosecution, said the six men "plotted and conspired homicide". The killer of Mr Larsen has not been identified yet and the prosecution will try to convince the 12-man jury that the bikers should be sentenced as a group, not as individuals. If found guilty, the six face up to life in prison.
Sixty-nine people are scheduled to take the stand, including a non-biker considered the key witness. The witness tried to avoid making a court appearance because he was scared by threats from the Hell's Angels, but the Supreme Court ruled in September that he must testify.Reuse content