NBC news -- Three college friends of Boston Marathon bombing suspect Dzhokhar Tsarnaev are under arrest, suspected of removing items from his dorm room after the April 15 attack, sources said Wednesday.
Two of the pals were detained April 20 on immigration charges and a third has now been taken into custody, sources said. They are expected to face obstruction of justice charges, the sources said.
NBC's Pete Williams and Michael Isikoff report on the arrests made in connection with the bombing.
There was no indication the three University of Massachusetts-Dartmouth students had any prior knowledge of the bombing.
"Please be advised that there is no threat to public safety," the Boston Police Department said on its website, confirming the arrests but releasing no further information.
Authorities said Dzhokhar Tsarnaev, 19, and his older brother Tamerlan carried out the blasts that killed three and wounded more than 200 near the finish line of the race.
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.
Pete Williams and Tracy Connor, NBC News