. >> reporter: as boston remans a city in grief tuesday with a 15-block crime scene at its center, president obama vowed those responsible would be caught and brought to justice. >> what we don't yet know is who carried out this attack or why, whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual. but we will find out. we will find whoever harmed our citizens. and we will bring them to justice. >> a lot of questions in the beginning of a major investigation. and brian, as if this wasn't enough, there is what appears to be another terrorist scare. this one in washington. what's going on? >> a suspicious letter sent to mississippi senator roger rickart. it had a white granular substance, two field tests indicated it was ricin, a highly poisonous substance. it's been sent to a lab to do full tests and we'll know the result of tests tomorrow. >> it could shake up the delivery of mail? >> it could shake up the delivery of mail but at this point, there's no indication it's connected to what's happening here. >> thank you ver