The findings contrast with a previously released, independent report, and says fewer militants staged the attack than commonly believed.
Most of the more than 330 people who died during the three-day Beslan school siege were killed during the fiery conclusion that unfolded after gunfire broke out between hostage takers and Russian security forces.
Since then, survivors, victims' relatives, and experts have accused the Russian leadership of covering up for what they call a botched rescue effort by security forces.
Russian Forces Exonerated
But today, commission head Aleksandr Torshin, speaking before the Federation Council, said Russian security forces were working to save people.
"It has been established that one of the gang members set off a home-made explosive device in the gym of School No. 1, as planned in advance," Torshin said. "This is a key episode that is being disputed by those who try to accuse federal authorities of trying to storm [the school] and to make [authorities] responsible for the explosion. However, the commission, based on numerous examinations and testimonies, has established officially that the explosion was caused by the actions of the terrorists."
In September, Yury Savelyev, an explosives expert who participated in the parliamentary inquiry, accused the commission of "hiding the truth." His own, independent report alleged that Russian security forces were responsible for two explosions that triggered the storming of the school.
Savelyev's revelations led Torshin in September to delay the release of the parliamentary commission's report until the new claims could be investigated.
Its release today revealed that the commission believes 32 militants took part in the attack, as opposed to the 78 attackers mentioned in Savelyev's report.
Not Everyone Satisfied
The head of the Beslan Mothers Committee, Susanna Dudiyeva, harshly criticized the new report today during a telephone interview with RFE/RL's Russian Service.
"I am outraged with the commission itself that was given such authority but has proven only capable of solidarity with officials," Dudiyeva said. "Their categorical claim that there were exactly 32 terrorists has no proof. The people who were held hostage at the school say there were many more of them."
Torshin also announced today that the commission determined the attack was masterminded by Chechen and foreign militants.
"The act of hostage taking on September 1 to 3, 2004, was carefully planned by the leaders of the terrorist underground and it had been prepared long before it was carried out," he said. "The terrorist act in Beslan was organized by [former Chechen rebel leaders] [Aslan] Maskhadov, [Shamil] Basayev, Abu Dzeit and Khashiyev. The actual execution of the terrorist act was led by Khuchbarov, alias 'the Colonel.'"
Maskhadov and Basayev have since been killed:
Answering journalists' questions, Torshin said many of the hostage-takers were on drugs at the time of the attack.
(compiled from agency reports)