Boston police have three additional suspects in custody in connection to the Boston Marathon bombings, the Boston Police Department confirmed Tuesday.

A spokeswoman at the department directed all questions related to the suspects to the FBI, which has yet to disclose their identities. The Boston Globe, citing an unnamed police source, reports that the suspects are three college students and that they are suspected of aiding Dzhokhar Tsarnaev after he allegedly bombed the marathon.

NBC’s Pete Williams reported that the three have been under FBI surveillance for 10 days. The suspects were roommates with Dzhokhar in college, according to Williams.

Tsarnaev, a 19-year-old college student, is charged with killing three and injuring more than 200 in the two bombs last month. His older brother and suspected co-bomber, Tamerlan Tsarnaev, was killed while fleeing arrest.

In a statement, the police department said there was no threat to public safety at this time.