minutes later, another blast. the following day, reveals the full horror. the black widow's brother driving a car bomb blew this fire truck apart. callus timing killing the emergency service workers, just as they arrived to put out the flames. a brutal conflict spilling over from neighboring chechnya, playing out as tamerlan tsarnaev visited his parents here last year. this is the same checkpoint, we can't stop here, back then the attack struck fear into the security services. according to local journalists for a while, police were too afraid to patrol. a terror defense lawyer tell me russian short authorities are handling the female bombers all wrong. >> it's not criminal problem. it's social problem. >> reporter: it is a problem that's been around over a decade involving wives of rebels killed by government forces.