Nur-Pashi Kulayev was one of 32 militants who attacked the school, taking more than 1,100 students and staff hostage on the first day of classes September 1.
Most of the hostages were rescued as security forces stormed the building September 3, but 318 died, including 186 children. All but one of the attackers are believed to have also died.
Kulayev's defense lawyer and a group of survivors and relatives of the siege victims filed appeals in May after a regional court found the suspect guilty on eight charges, including terrorism, murder and illegal arms possession, and sentenced him to life in prison.
The Voice of Beslan group believes the security forces should be held partly responsible for the loss of life, claiming that the death toll could have been much lower had they not opened fire on the school building.
"We believe the security forces are to blame for the children's deaths, along with Kulayev, but they still go unpunished. The case file does not say a word about the flame throwers and the tanks used in storming the school, and all witness testimonies are being kept off the record," Ella Kesayeva, a Voice of Beslan activist, said.
A Russian parliamentary commission investigating the Beslan school siege has dismissed allegations that the rescue operation was botched and cost many lives.
In a final report released last Friday, the commission admitted local law-enforcement officials ignored orders from Moscow to improve school security.
However, it said there was no evidence to prove the building had been fired on by security forces, and that explosions during the storming had been caused by grenades thrown from the outside rather than by bombs set off by the terrorists inside.
"We do not trust [commission head Alexander] Torshin. The commission's conclusions, presented as assertions, are all highly opinionated and uncorroborated," Kesayeva said. "We insist on a retrial, we just want the verdict to be based on evidence, not groundless claims."
