THE human cost is clear, even if the cause is baffling. A bombing on the Minsk metro yesterday killed at least 12 people and injured more than 200. Lenta.ru has an excellent piece (link in Russian) giving the details and some analysis. The bomb seems to have exploded under a bench on the platform of the Oktyabrskaya station, one of the busiest on the network, as two trains were in the station. It was a big bomb, equivalent to 5kg of TNT.

Political violence in Minsk is rare, though not unknown. Ten years ago, four people went missing. They are believed killed by the authorities. Since then opposition demonstrations have regularly been broken up roughly and opposition activists treated nastily; but the worst that happens is broken bones, not fatalities. A mysterious bomb in 2008 injured dozens. Nobody claimed responsibility.

In other countries, the finger of suspicion for the latest bomb would point immediately to Islamist terrorists. But they seem a highly unlikely culprit. Belarus has stayed clear of Russia's war in Chechnya, so attracts no jihadist ire for that. It has no significant Muslim population (just a handful of Tatars, and some Soviet-era Iraqis, both highly integrated). Terrorists from the north Caucasus tend to be suicide bombers.

It is hard to see why anyone in the mainstream opposition would be behind the outrage. It does not destabilise the regime. It would carry huge risks to the perpetrators. And it would be completely out of character. Belarusian opposition activists have many flaws: too fond of conferences in the West, too inactive when it comes to campaigning at home. But the worst that can be said of them is that they are marginal, not murderous.

A slighly more plausible candidate would be an extremist movement. Belarus has no real tradition of political radicalism. Russia has skinheads, persecutors of ethnic minorities and even neo-Nazis (puzzling: do they think they are übermenschen or untermenschen?). Such groups have minor offshoots in Belarus. Perhaps one such is showing off its abilities, for purposes of its own.

A Belarusian outfit called the "White Legion" was linked to the 2008 bombings and may have had a hand in two earlier explosions in 2005. But nobody knows much about it. Some even doubt it exists. In ex-communist countries, such bogeys are sometimes conjured up by clandestine sponsorship from ill-wishers, inside the country or abroad. On investigation, they prove to have ectoplasmic properties.

Splits within the regime are a possibility. The arrest in December 2010 of Igor Azarenok, the air-force chief, remains a mystery, and may be resented by his friends. Some analysts posit the existence of rival factions of "young wolves" and "old wolves" (the former friends of Mr Lukashenka's son Viktar, the others old KGB men).

Another analysis involves a hardline faction determined to push Belarus further towards autocracy and away from the West. Supposedly, it outguns another (equally hypothetical) pro-European faction, by rattling the nerves of the country's erratic leader, Alyaksandr Lukashenka (to give his name the Belarusian spelling: in Russian he would be Aleksandr Lukashenko).

Such secret internal machinations can of course explain almost anything. But it would be nice to have some evidence. In this case little exists. The last bombing prompted a curiously leisurely reaction from the authorities, but was followed by the speedy sacking of Viktar Sheiman, at the time Mr Lukashenka's powerful security chief.

Still, Mr Lukashenka could presumably have fired him anyway (he has regularly shown little hesitation in purging his inner circle of supposedly powerful people). The idea that the regime needs to let bombs off in order to have an excuse for a reshuffle sounds batty. So is the idea that the bomb was designed to distract public opinion from the country's economic woes.

The opposition worries that the bomb will be used as an excuse for another crackdown. And so it may. (The 2008 bombing was the precursor to a compulsory fingerprinting programme.) But the authorities have been cracking down quite hard already. It is hard to see how the bomb adds a vital pretext. In 1999, apartment-block bombings in Moscow and elsewhere prompted a climate of near-panic, amid which (coincidentally or not) the previously unknown new prime minister Vladimir Putin suddenly became the most popular politician in the country. But Mr Lukashenka is popular already.

The result is a hall of mirrors: did the authorities let off a bomb hoping to discredit the opposition? Or did the opposition do it in the belief that the authorities would take the blame? Or was it the Russians, for some conspiracy theorists the all-purpose malefactors? Did the regime do it in order to highlight the threat from "extremists", or in the hope of pinning blame on outsiders? Or was it NATO: after all, the wicked Westerners have bombed Libya, so why not Belarus? The explanations become steadily more absurd and inconclusive.

The only hard fact so far is that the bombing was a professional job, callously executed. Mr Lukashenka took his usual fatherly line, attending the scene of the blast with his six-year-old son (his companion in almost all public appearances).

He linked the blast to the bombing in 2008, saying "these are perhaps links in a single chain". He asked who benefited from undermining stability, and added: "I do not rule out that this was a gift from abroad." Politics in Belarus is always opaque. Now the tint of innocent blood renders it murky and sinister.