Of the many questions that have yet to be answered in the marathon bombing investigation, the toughest question may be: Why?
News reports indicate Tamerlan Tsarnaev, 26, exerted a lot of influence on his 19-year-old brother Dzhokhar Tsarnaev.
Investigators say Tamerlan did frequent jihadi websites, but Dzhokhar’s friends say he was not a Muslim radical.