Belarussian authorities said Tuesday that they have identified a key suspect and detained three others in a deadly blast in the Minsk metro that they called a terrorist attack.
But the Monday evening bombing, which killed at least 12 and injured more than 150 in the Oktyabrskaya metro station, baffled experts because of the absence of any compelling theory of who could be to blame.
"This is the most mysterious terror attack I have ever heard of," Alexei Malashenko, an analyst with the Carnegie Moscow Center, said by telephone.
By all accounts, it is the first deadly terrorist attack in Belarus since the country gained independence in 1991.
Opposition activists voiced fears that the authoritarian regime of President Alexander Lukashenko would use the explosion as a pretext for a new round of repression.
Lukashenko, who has come under pressure from the West for a violent crackdown after his re-election last December, said the perpetrators should be sought at home and abroad.
"This might be a present from outside, but we must also look among us," he said in comments carried by Interfax late Monday.
Experts said that neither the country's embattled opposition nor Muslim fundamentalists or radical nationalists were likely to blame. Belarus only has a tiny Muslim population and has never taken part in operations against Islamist insurgents.
"To imagine that Doku Umarov would send terrorists to Minsk is just ridiculous," Malashenko said, referring to the North Caucasus rebel leader who has taken responsibility of recent bombings in Moscow, including the double suicide attack in the metro that killed 40 people in March 2010.
This leaves murky theories of a lone attacker or an "inside job" involving Belarus' security services, the KGB — and experts tended to support the latter.
The KGB said in a statement Tuesday that the bomb contained explosives equivalent to 5 kilograms of TNT.
Media reports said the blast left a 1-meter-deep crater on the subway platform.
The country's interior minister, Anatoly Kuleshov, told a news briefing that the device was most probably radio-controlled.
The minister did not elaborate, but a source in the Belarussian presidential administration told Interfax that the bomb was hidden under a platform bench and went off opposite a train car while passengers were disembarking during the evening rush hour.
Andrei Soldatov, head of the Agentura.ru security think tank, said those who carried out the bombing must have had considerable resources. "An attack on such scale could only be committed by a group of relatively experienced people," he said by telephone.
Interior Minister Kuleshov said there were at least two male suspects.
"We have prepared a facial composite of two people, but that is not the end," he said, according to a video transcript posted on his ministry's web site.
No composites were released immediately, but KGB chief Vadim Zaitsev confirmed the authenticity of a photo published by the Lifenews.ru tabloid. "This is real," he said, Interfax reported.
Zaitsev described the prime suspect as a strongly built man aged under 27, 175 to 178 centimeters tall, dressed in a brown jacket and brown cap.
"We do not exclude that he had accomplices," he told reporters in Minsk.
Zaitsev added that three people had been detained and were being questioned in connection with the blast. It was unclear whether the three were also suspects.
He also said investigators were considering three possible motives for the blast: to destabilize the country, revenge from an extremist group, or the act of a "sick person," RIA-Novosti reported.
Analysts said that in light of the tense political and economic situation in Belarus, a political motive was most likely.
Leading opposition activists have languished in prison after police violently suppressed their mass protests amid complaints that the Dec. 19 presidential election was rigged. More recently, the country has faced new financial turmoil and a run on foreign currency.
The only other major attack in Minsk occurred in July 2008 when a bomb blast injured 50 people at a concert attended by Lukashenko. No arrests have been made in the case.
Joerg Forbrig, a Belarus specialist with the German Marshall Fund in Berlin, said the Belarussian government was most likely to benefit from the latest attack.
He said it would provide a temporarily distraction from the country's domestic troubles and, more important, possibly make it more difficult for the European Union to impose sanctions on the country.
"The necessary consensus will probably become even harder because reluctant member states can bring forward a compassion argument," Forbrig said in e-mailed comments.
The 27 EU members are due to decide on sanctions as a reaction to the political repression in Belarus following last December's crackdown.
Forbrig said Moscow might also feel more inclined than before to extend loans to Minsk. "There will be more sympathy to help the brotherly nation in an hour of need," he said.
Moscow and Minsk have been locked in a union state for years, but relations have been strained amid erratic behavior by Lukashenko and spats over gas subsidies.
All this leads to the question of whether the Belarussian leadership is behind the blast. "Given Lukashenko's words and deeds over the past years, this is by no means absurd," Forbrig said.
Yaroslav Romanchuk, an opposition activist who ran in last December's election, said the government needs to show resolve to refute such speculation. "It is a good sign that they have invited foreign specialists to help in the investigation," he said by telephone from Minsk.
The Belarussian Foreign Ministry said experts from the Federal Security Service were already aiding investigators and that specialists from Israel would arrive soon, Interfax reported.
Romanchuk also said the attack was a chance for political reconciliation. "Now is the time for negotiations to reset trust in the government," he said.
But in a sign that fears of a new crackdown were not unfounded, KGB agents on Tuesday searched one of the country's main independent newspapers, Nasha Niva. "They are blockading us in the editorial offices and demanding the paper turn over videos taken at the blast site," editor Andrei Skurko told The Associated Press.
The Belarussian Prosecutor General's Office warned the media to stop releasing "irresponsible libelous publications" about the blast.
"We warn everybody who uses the tragic events for speculative goals that they will be held responsible under the current law," the office said in a statement on its web site.