Nur-Pashi Kulayev stared out from inside a metal defendant's cage in the courtroom where he faces charges of murder and terrorism.
Mr. Kulayev is the only one of about 30 militants who was not killed by Russian troops when the school siege ended in chaotic shooting.
The young man reportedly admits taking part in the raid on School Number 1 in the town of Beslan last September, but maintains that he personally did not kill anyone.
Security was tight with policemen deployed all around the courthouse in the southern Russian city of Vladikavkaz, capital of the region where the dramatic siege took place.
About 1,500 people were taken hostage by heavily-armed militants who broke up an outdoor ceremony celebrating the start of the school year and forced mostly women and children into the school gymnasium.
The siege ended two-days later after several explosions set off chaotic shooting as hundreds of bloodied, half-naked children fled for their lives.
Nikolai Shapel, the local prosecutor trying the case, said it was difficult to read through all the names of those who died, as well as the events that occurred during the siege.
Authorities had difficulty finding any lawyer who would defend Mr. Kulayev, and ultimately a court-appointed attorney was compelled to take the case.
If convicted, Mr. Kulayev faces a maximum of life in prison because Russia imposed a moratorium on the death penalty in 1996 when it joined the human-rights organization known as the Council of Europe.
Relatives of those who died were seen weeping near the courthouse as the trial started, many holding pictures of their children or other loved ones. Some told local reporters they would like to exact their own revenge on the man.
The Beslan siege was the worst terrorist incident in Russia related to the ongoing war in breakaway Chechnya, where Russian troops have been battling separatist rebels for more than a decade.
Mr. Kulayev is from Chechnya, although many of the other militants were from Ingushetia as well as North Ossetia, where Beslan is located.