A videotape obtained by the Mothers of Beslan group offers new evidence that a botched raid by government agents triggered the Beslan massacre, Susanna Dudiyeva, head of the group, said Friday.

More than 330 people, of whom more than half were children, were killed in the explosions and gunfire that erupted during the hostage-taking crisis in 2004.

The videotape calls into question official explanations of events, Dudiyeva said. The government maintains that the bloodshed was triggered by the explosion of one of the hostage-takers' homemade bombs inside the school gymnasium where hostages were being held.

"This supports the theory that the source of the first explosions came from outside," she said by telephone from Beslan.

The tape was screened for journalists in North Ossetia on Thursday. The Moscow Times was not able to obtain a copy as of Sunday.

According to a transcript on the Mothers of Beslan web site, the videotape shows two bomb squad officers being questioned by an unnamed law-enforcement official just after they had defused the hostage-takers' remaining bombs after the firefight on Sept. 3, 2004, the day of the massacre.

One of the officers, identified as Bagatir Nabiyev, tells the official that the terrorists' bombs could not have gone off inside the gymnasium because in this case the hostages' bodies would have been riddled with shrapnel from the bombs. He also says a hole in the wall came from an explosion outside, and not inside the gymnasium.

"So there were no explosions on the premises?" the official asks, according to the transcript.

"On the premises, there were no explosions," is Nabiyev's answer.

Mothers of Beslan and other activist groups believe the carnage began when government agents fired grenade launchers at the gymnasium.

Two official investigations, one by prosecutors and one by a parliamentary commission, have concluded that hostage-takers, not security forces, triggered the firefight.

But a dissenting member of the commission, Duma Deputy Yury Savelyev, released an independent report in 2006 stating that security forces started the battle by firing rocket-propelled grenades at the gymnasium.

The videotape was mailed to Mothers of Beslan by an anonymous source, Dudiyeva said.

Dudiyeva believes the footage was previously kept secret to cover up official bungling.

"If prosecutors were interested in an objective investigation, they should have looked into this," she said, adding that a copy of the videotape had been given to a prosecutors' office task force investigating the Beslan attack.

A spokeswoman for prosecutors in Vladikavkaz, the North Ossetian capital where the task force is based, said Friday afternoon that nobody in the office was available for comment. She could not confirm whether the videotape had been received.

Marina Litvinovich, who runs the Truth of Beslan web site, said the emergence of the videotape was unlikely to change the official version of events.

"This is not the first document or videotape that relatives of the victims have handed over to investigators," she said. "Investigators have received many such things, but nothing, unfortunately, has been able to change their position."

Critics of the official version of events have charged that the Federal Security Service may have ordered the raid of the school and has been interfering with the investigations.

"To this day, not a single FSB agent has been questioned," Dudiyeva said. She said Mothers of Beslan had sent a petition to the FSB asking them to release any classified video materials about the Beslan raid.

An FSB spokesman said Friday that he could not immediately comment and asked for questions to be submitted in writing. Faxes sent to the FSB did not go through on Friday afternoon.

Dudiyeva said it is important to find out who gave the order to raid the school.

"If nobody is punished for these bungled orders, for the fact that armchair generals direct these operations, then this could happen to any child," she said.