Many of the relatives of those killed at the bloody school siege in September, 2004, have never believed the official version of events.
An initial inquiry concluded that the fiery conclusion to the crisis was caused by explosions inside the school hall, where Chechen separatists had held more than 1,000 people, most of them children, hostage for three days.
Now a video posted anonymously and linked to the Beslan Mothers Committee website appears to show that the explosions were caused by weapons fired from outside the building, where Russian special forces were preparing to storm the school on the third day.
Over 330 victims, more than half of them children, were killed in the siege, which ended in chaos when security forces stormed the sports hall to free the children and parents.
Aneta Gadiyeva, a member of the Beslan Mothers Committee who lost her daughter in the massacre, says the video supports her theory that security forces fired two grenade rounds on the school gymnasium, starting a fire that then engulfed the building.
She told RFE/RL that the committee is appealing to investigators to watch the video: "We are once again appealing to the authorities to make this tape available to investigators, although in fact they had this tape, but they did not take it into consideration. For some reason they decided not to include this tape [in the investigation]."
Marina Litvinovich, the editor of the Truth about Beslan website, told RFE/RL the video refutes the official version of events.
"[This tape] confirms the original version of the events that unfolded in the Beslan school on September 3: that the explosions came not from the hostage-takers within the hall, but that the school was targeted by machine-gun fire and grenades from outside the hall," Litvinovich said.
In the video, children are seen running from the building before two loud blasts are heard -- apparently from outside the sports hall. But last year, the official commission into the Beslan tragedy vindicated the security forces and said that the explosions were caused by the hostage-takers, who set off booby traps.
Families of those killed in the school siege are still waiting for investigators to deliver a final report on the tragedy. But they say the video they have received supports their theory that there has been an official cover-up.
An independent report by explosives expert Yury Savelyev alleged that Russian security forces were responsible for two explosions that triggered the storming of the school.
"It confirms the original version...that the explosions came not from the hostage-takers within the hall, but that the school was targeted by machine-gun fire and grenades from outside."
Sergei Markedonov, a political analyst at the Institute for Political and Military Analysis and an expert on the Caucasus region, said he can't understand why the authorities have not taken some responsibility for what happened.
"I think that unfortunately September 1 will forever be associated with the events of Beslan, and it seems to me that there are some serious lessons to be learned from this. It seems to me that the head of the Russian government could participate more fully in the events of Beslan," Markedonov said.
The only hostage-taker officials say survived the siege, Nurpashi Kulayev, was jailed last year for life for his part in the siege.
(RFE/RL's North Caucasus and Russian services contributed to this report. With additional material from Reuters.)