The suicide bomber who killed at least 14 people in an attack Monday on a crowded Russian commuter bus likely got on and walked to the back of the bus before detonating high explosives, according to a former FBI bomb technician with experience operating in Russia.
Monday's attack in Volgograd in the southern reaches of Russia followed a similar explosion there at a train station on Sunday. The identity of the attackers is not year clear, though Islamic extremist groups from Chechnya have said they would be conducting such acts of terrorism ahead of the Olympic games in nearby Sochi in roughly a month.
At least 30 have died in the joint attacks.
The size and effect of both bomb detonations indicate the attackers used high explosives, such as semtex, says Paul Fennewald, a former special agent with the FBI. The use of such military-grade explosives and the style of the attack, including the use of female suicide bombers, is consistent with previous attacks by Chechen extremists.
"By attacking a transportation system – two different modes of transportation – they're sending a pretty loud message to people to be afraid," says Fennewald. Reports of shrapnel packed into the explosives indicates the attackers intended to kill as many people as possible, not just inflict fear.
Footage of Sunday's attack at the train station shows a quick red flash followed immediately by gray smoke and a massive shock wave as gas instantly builds up in the enclosed stone building and expands rapidly outward.
The bus bombing on Monday inflicted the most damage on the rear of the bus, which was likely also the location of the detonation, says Fennewald. The attacker could have walked to the back of the bus and waited before detonating, making it more difficult for investigators to trace where he got on. That person could just as easily have left a backpack behind and got off the bus instead of killing themselves, he says.
"It's someone dedicated, and ready to show they're dedicated," Fennewald says.
The Russian government has not yet asked the U.S. for assistance in investigating this attack, says Pentagon spokesman Army Col. Steven Warren. Participation in joint exercises, such as the Operation Vigilant Eagle counterterrorism exercise beginning in 2009, has brought the two governments' law enforcement arms together, he says.
"The mil-to-mil relationship...is as good as it's ever been," he said Monday afternoon.
The U.S. continues to share intelligence with Russian counterparts, he added, declining to comment further.
Chechen rebel leader Doku Umarov has threatened in recent months to carry out attacks against the Russian government as it prepares to host the 2014 Winter Olympics.