Boston Police said Wednesday they have arrested three more people in the marathon bombing investigation, but gave no additional details.
Sources told NBC News the three are college roommates of accused bomber Dzokhar Tsarnaev and are suspected of removing items from his dorm at the University of Massachusetts-Dartmouth.
There was no indication they had any prior knowledge of the bombing. Sources said the FBI had been investigating them for about 10 days.
"Please be advised that there is not threat to public safety," the Boston Police Department said on its website.
Authorities said Dzhokhar Tsarnaev, 19, and his older brother Tamerlan carried out the blasts that killed three and wounded more than 200.
Tamerlan Tsarnaev, 26, was killed during a firefight with police. Dzhokhar was arrested after a manhunt and has been charged with using a weapon of mass destruction.
Law enforcement officials have told NBC News that Dzhokhar told them during questioning he and his brother wanted to defend Islam after the American wars in Iraq and Afghanistan.
The brothers, ethnic Chechens who had been living in the U.S. for more than a decade, were seen on video at the marathon. Investigators have been trying to determine if they received assistance from anyone else in the U.S. or abroad.
