"We've found that one of the judges in the case was biased. According to the rules, the case is to be sent back to the district court. There is to be a retrial," Fredrik Wersäll, president of the Svea Court of Appeal, told the TT news agency on Thursday.
According to a statement issued by the appeals court, one of the district court lay judges was also a representative on the Södertälje police board at the time of the trial and as a result is considered to have been biased.
The initial request for a retrial was filed by the 31-year-old man who was sentenced to life in prison for murder, incitement to murder, kidnapping, aggravated extortion, and a host of other charges.
The guilty verdicts were delivered in August, concluding a trial which had lasted roughly half a year.
Seventeen other people were convicted, considered one of Sweden's largest and most expensive criminal investigations and trials ever, costing around 200 million kronor ($30 million), according to estimates by Sveriges Radio (SR).
The 31-year-old had been convicted for ordering three murders, something he was able to do, according to prosecutors, because he was the leader of a criminal syndicate known as the "Södertälje Network".
However, the 31-year-old has continually claimed that the "Network" doesn't exist and that he has never been a gang leader.
He, along with everyone else convicted in the case, as well as prosecutors, had appealed the district court ruling.
But instead of ruling on the case, the appeals court has instead ordered a retrial.
"One of the judges, a lay judge, was at first a substitute and then a full representative on the police board in Södertälje when the trial was ongoing. The question is whether the efforts of the Södertälje police were discussed at basically every meeting. For an outsider, it must seem that it would be hard to be a board member and not be involved in the police's assessments," said Wersäll.
Gunnar Appelgren, who led the police investigation in Södertälje, was shocked by the news that a retrial had been ordered.
"I'm very surprised. That's going to mean a lot of work for a lot of people," he told the TT news agency.
In his eyes, the existence of the "Södertälje Network" is commonly accepted knowledge.
"The Swedish people have received the same information via the media, that we in the police believe there is a network. You can't find anyone that doesn't think that way," said Appelgren.
The defence attorney for the convicted 31-year-old welcomed the news.
"It's incredibly good news," Fredrik Ungerfält told TT, explaining that the lay judge apparently failed to properly carry out his responsibility to ensure he was "impartial and independent".
Wersäll of the appeals court said it was a hard decision for the three judges who ruled on the retrial request.
"It's going to mean a lot of discomfort for everyone involved, both the victims, witnesses, and the accused," he said.
The case stems from the December 2009 killing of the leader of the rival X-team criminal gang in at the gambling club Oasen in Södertälje.
The slaying was the catalyst for a several years of bloody conflict between the gangs which police inspector Thomas Nordström characterized as a battle for control of the drugs trade in the area.
In the spring of 2010, a car was fired upon in Södertälje, and the 31-year-old is believed to have been the target.
According to police, the "Network" gang took exacted revenge by having young Assyriska FF footballer Eddie Moussa and his brother gunned down by assailants wielding automatic weapons at the Oasen club later that year.