Investigators are ramping up their focus on Katherine Russell, the widow of Boston Marathon bombing suspect and alleged planner Tamerlan Tsarnaev after an inspection of her computer turned up radical Islamist material, law enforcement sources said. With Dzhokhar Tsarnaev, 19, alive and in custody, police are trying to determine what involvement, if any, Russell had in the plot to plant bombs at the finish line of the Boston Marathon on April 15. Russell’s attorney, Amato DeLuca, released a statement earlier this week saying his client was willing to provide “as much assistance to the investigation as she can.” The younger...