On May 16, the court ruled Nurpashi Kulayev, said to be the sole surviving hostage taker, had committed a terrorist act, murder, and attempted murder, and was also a member of an illegal armed group.
The reading of the verdict, which also includes an assessment of evidence, is expected to continue for several days.
Prosecutors have demanded the death penalty for Kulayev, although Russia has a moratorium on capital punishment.
The Beslan raid resulted in the deaths of 331 people, more than half of them children. Victims' relatives have accused authorities of botching up the rescue operation.