Legal experts say authorities are placing intense pressure on the widow of one Boston Marathon bomber and three detained friends of the other to cooperate in the ongoing investigation.
Federal agents follow the widow of Tamerlan Tsarnaev in unmarked vehicles when she leaves her parents' Rhode Island home. The college buddies of surviving suspect Dzhokhar Tsarnaev face more than five years in prison after being jailed on charges related to covering up his activities.
The experts say investigators are trying not just to determine whether widow Katherine Russell and the friends are culpable but also to force them to share all they know about the brothers and possibly a wider plot.
Russell's lawyers say she's speaking with FBI agents. The students' attorneys say their clients didn't know about the plot.