Tazhayakov was a student at the University of Massachusetts Dartmouth when he left the U.S. in December. In early January, his student visa status was terminated because he was academically dismissed by the university.
Peter Boogaard, a DHS spokesman, said Wednesday that when Tazhayakov arrived in January Customs and Border Protection had not been alerted that he was no longer a student. Boogaard said the department was working on a fix to the student visa system.
The third student arrested, Robel Phillipos, was charged with willfully making materially false statements to federal law enforcement officials during a terrorism investigation.
All three men charged in connection with the case began attending UMass Dartmouth with Tsarnaev in 2011, according to the FBI.
If convicted, Kadyrbayev and Tazhayakov could get up to five years in prison and a $250,000 fine. Phillipos faces a maximum of eight years behind bars and a $250,000 fine.
The lawyers for the Kazakh students said their clients had nothing to do with the bombing and were just as shocked by it as everyone else. Phillipos' attorney said the only allegation against him was "he made a misrepresentation."
In other developments:
— Police and politicians across the U.S. are pointing to the example of surveillance video that was used to help identify the Boston Marathon bombing suspects as a reason to get more electronic eyes on their streets. They want to gain police access to cameras used to monitor traffic, expand surveillance networks in some major cities and enable officers to get regular access to security footage at businesses.
— At an interfaith service Thursday night, a member of the executive board of the mosque where the bombing suspects prayed condemned the attacks. Anwar Kazmi said the bombings were a "grotesque perversion of the teaching of our faith."