The school bell rang at 9.15am to mark the moment when evil arrived in Beslan. The women gathered in the shattered sports hall at School Number One reacted with a collective groan that dissolved into sobbing appeals to their dead children, staring back at them from photographs on the walls.

On the anniversary of the attack that left 186 children among 344 people dead, Beslan remains trapped in those three days that ended with a massacre as Russian troops battled a gang holding 1,200 hostages on the orders of Shamil Basayev, the Chechen warlord. The mourners’ tears are laced with bitterness that so many questions remain unanswered.

An investigation by the Russian Prosecutor-General drags on, fuelling anger that there is a Kremlin cover-up to protect the security services from allegations of incompetence. Vladimir Khodov, head of the town’s administration, told The Times: “The investigation is not telling us the truth, lots of information is kept hidden. We want to know who among our officials was guilty of allowing the murder of so many children.”

Among the mysteries are why the terrorists attacked a school only 200m (218 yards) from Beslan’s main police station, ignoring others en route, and how they apparently knew that its celebration to mark the first day of term had been brought forward by an hour.

Official reports identified 32 terrorists but witnesses are certain there were more. The sole survivor, Nurpa-shi Kulayev, jailed for life, is the only person convicted so far.

Most crucial is the question of who began the firefight. A parliamentary commission said in December that the terrorists detonated a bomb in the school, forcing troops to respond. The Beslan Mothers’ Committee insists that Russian forces fired first. The relatives’ campaign group obtained previously unseen official videotape in July that appeared to confirm this.

A dissident member of the commission, Yuri Savelyev, a weapons expert, announced that special forces fired rocket-propelled grenades at the school in a botched raid. “The Prosecutor-General’s Office has been silent about the video so far, but we are not going to leave this alone,” said Susan-na Dudiyeva, chairman of the mothers’ committee, who lost her 13-year-old son. “If we agreed that only the terrorists were responsible then we would calm down. But we are convinced that the authorities let this terrorist act happen and that they failed to save people.”

Mrs Dudiyeva wants to forge links with groups representing victims of the terror attacks in New York, London and Madrid to raise pressure on the Kremlin. She regrets that she and other parents did not rush into the school as soon as their children were taken hostage.

She said: “Some people would have died but maybe the children could have run away. At least we would not have let them suffer for so long.”

Absent from the memorial ceremony was Lidia Tsaliyeva, the former headmistress, who has become a hate figure for some grieving relatives, despite 52 years’ service. They allege that she hired strangers to repair the school in the summer holidays and that the workmen stockpiled weapons for the terrorists. Mrs Dudiyeva said: “I despise her and consider her guilty, although the prosecutor would not investigate whether weapons were hidden.” Mrs Tsaliyeva, 73, insisted to The Times that she had employed only local workers. She and two grand-children were among the hostages who survived.

There are plans to demolish the school and build a cathedral, leaving the gym as a memorial to the dead.

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