The blast which devastated an apartment building in the southern Russian city of Volgodonsk was the latest in a series of explosions in Russia which have killed more than 200 people.

	Who is to blame? What Russia can do Timeline: The blasts which shook Russia

Two blasts in Moscow led to a massive security sweep through the city, and police said there was a suspect behind what they believed to have been bomb attacks.

He was a bespectacled man of North Caucasian appearance who was renting office space in the ground floors of the two apartment blocks, which were about six kilometres apart in the south-east of Moscow.

The suspect was carrying a passport with the name Mukhit Laipanov, which appears to be false.

The real Mukhit Laipanov is reported to have died in a road accident last February in the Stavropol region of southern Russia.

The Laipanov connection looks like persuasive evidence of a North Caucasian link.

Yet that still does not explain who carried out the Moscow bomb attacks or why.

Chechen denials

The Chechen president Aslan Maskhadov has condemned all acts of violence in Russia - and with good reason.

Such outrages will make life much more difficult for ordinary North Caucasians in Moscow and further undermine President Maskhadov's hopes of resuming negotiations with the Russian government.

The name of the Arab fighter Khatab is often mentioned.

He recently vowed "retaliation" against Russia after Russian forces captured two Islamist villages in Dagestan.

The weekly newspaper Novaya Gazeta also named him as a suspect. It reported that it had evidence that the guerillas who have been fighting Russian forces in Dagestan were behind the Moscow bombs and that a group of 30 men, most of them Russians, had been recruited to carry out the attacks by Khatab.

And yet the man who was leading the rebellion in Dagestan, Shamil Basayev has disclaimed any responsibility.

In an interview with Agence France Press in Chechnya he rejected the suggestion that either he or Khatab were behind the blasts.

Certainly it is hard to think of any political or military advantage which could be gained by the rebels in blowing up a Moscow apartment block and killing civilians.

Anyone wanting to fight a war with Russia would be more likely to choose a government or military target in the capital.

Searching for answers

So there are still many unanswered questions in this tragedy.

Could it have been the work of a North Caucasian terrorist group working independently?

Could there be a political motive connected with the elections?

A growing mood of panic will make it harder to establish the truth.

In that atmosphere of tension some political forces in Russia stand to gain by the turmoil.