Dzhokar Tsarnaev, 19, was arrested Friday evening but has not been formally charged.
Government investigators have invoked the public safety exception, allowing them to question Tsarnaev before advising him of his Miranda rights, a Justice Department official says. Usually, suspects are told they have the right to remain silent and to have an attorney present during questioning.
"The last thing we should want is for him to remain silent," the senators said. "It is absolutely vital the suspect be questioned for intelligence gathering purposes."
It's "impossible" to consider the ethnic Chechen an enemy combatant, said Alan Dershowitz, a Harvard law professor.
"There's no way an American citizen committing a domestic crime in the city of Boston could be tried as an enemy combatant. It could never happen," he said.