Flink, who is in prison for killing seven people back in 1994, had sought to have his sentence reduced to 24 years.
According to the appeals court, Flink's crimes deserve a punishment longer than 24 years.
Flink is serving time for having shot seven people to death, including six members of the Swedish Women's Voluntary Defence Organization (Svenska Lottakåren), during a temporary, alcohol-induced psychosis.
A conscript ensign with the Swedish military and stationed in Falun in central Sweden at the time, Flink committed the murders with with his AK 5 service weapon.
In a precedent setting decision last spring, Sweden's Supreme Court (Högsta domstolen – HD) ruled that a lifetime prison sentence can, under special circumstances, be shortened to a maximum of 24 years.
According to the ruling, the primary factor for deciding to reduce a life sentence should be whether or not there is “a concrete and observable risk” that the convict may once again commit serious crimes.
Flink's time in prison has been without incident and the National Board of Forensic Medicine (Rättsmedicinalverket) recently judged Flink to have a low risk for recidivism.
But the Göta Court of Appeal found that his crimes warranted a punishment longer than 24 years.
Flink's lawyer, Johan Eriksson, told the TT news agency that he plans to appeal the decision to the Supreme Court.
“The precedent affirmed by the Supreme Court is crystal clear. The period of time which the Supreme Court has affirmed is that a life sentence can be reduced to between 18 and 24 years and nothing else. The only exception is if the person convicted is a danger to society,” he said.
“It can't be that Mattias Flink is the only person who isn't covered by the Supreme Court's ruling.”