Three of Dzhokhar Tsarnaev's friends have been charged in connection with the case.
Azamat Tazhayakov and Dias Kadyrbayev were charged Wednesday with conspiring to discard potentially incriminating items from Dzhokhar Tsarnaev's dorm room. Robel Phillipos was charged with making false statements to investigators.
The FBI is examining Dzhokhar Tsarnaev's laptop, two federal law enforcement officials told CNN.
Authorities have said they believe the brothers acted alone but are investigating whether they could have learned from or been aided by terror groups, including groups overseas.