They were detained April 20 after being questioned in connection with the attacks, but are not suspects, Stahl said. They are being detained at a county jail in Boston for violating their student visas by not regularly attending classes, he said.
The two, both students from Kazakhstan, had nothing to do with the attack and had seen no hints that their friend harbored any violent or terrorist sympathies, Stahl said.
Meanwhile, New York's police commissioner said the FBI was too slow to inform the city that the Boston Marathon suspects had been planning to bomb Times Square days after the attack at the race.
Federal investigators learned about the short-lived scheme from a hospitalized Dzhokhar Tsarnaev during a bedside interrogation that began Sunday night and extended into Monday morning, officials said. The information didn't reach the New York Police Department until Wednesday night.
"We did express our concerns over the lag," said police Commissioner Raymond Kelly.