The How And Why Stage

For federal authorities, the Boston Marathon bombing now moves into the how-and-why stage. The bombing and bloody chase that followed killed five people, including one of the suspects. FBI officials are trying to find out if and where the dead suspect, Tamerlan Tsarnaev, was radicalized. Investigators in Boston were able to communicate with his brother Sunday night. Dzhokhar Tsarnaev remains hospitalized with serious wounds. FBI agents are also trying toquestion Tamerlan's wife. The FBI says it investigated Tamerlan in 2011 upon a request from Russian intelligence officials.