many, many people traveling through that station at this time. >> according to available information, the explosion was carried out by the suicide bomber. she became nervous and activated the device. preliminary, the explosive was equivalent to 10 kilograms of tnt. >> another bomber blew herself up on a bus. now, this phenomenon of the female suicide bomber, black widows as they're called, is a hallmark of the fiekting insurgency that's raging in russia's north caucus region. that is very close to the area where the olympics will start in just a few weeks time. security there obviously extremely tight. but this region is big.