The European Court of Human Rights is due to rule on whether the Russian government should have done more to prevent a school siege in the city of Beslan in which more than 330 people died in 2004.
Chechen separatists took more than 1,000 hostages at School Number One, the vast majority of them children.
It ended when Russian security forces stormed the building. Survivors say the troops used excessive force.
A Russian inquiry stalled years ago.
No Russian official has been held responsible for the high number of deaths, which included 186 children.
The hostages were crammed into their school sports hall beneath explosives strung from the basketball hoops. Their captors were demanding Russian troops pull out of Chechnya.
The siege ended suddenly on the third day with two powerful and deadly explosions. Only one of the hostage takers was caught alive and put on trial.
For more than a decade, survivors and relatives have been asking whether the siege could have been prevented and whether so many people had to die in the rescue operation.
Survivors say the high death toll was due to the excessive force used by the Russian forces.
More than 400 of them have applied to the court in Strasbourg in the hope that it can deliver answers.