An FBI source said on Saturday that suspected Boston marathon bomber Tamerlan Tsarnaev built the bombs while his wife, Katherine Russell, was out working—and he was home with their 3-year-old daughter. It remains unclear if Russell played any role in plotting the attack, as she worked long hours as a home health aide while Tsarnaev stayed home with daughter Zahara. Neighbors said they often recalled Tsarnaev taking walks with his daughter. Tsarnaev, 26, died on April 19 after a shootout with police. His brother, 19-year-old Dzhokhar, told investigators that they learned how to build the pressure-cooker bombs from instructions in al Qaeda’s online magazine, Inspire.