(CNN) - Dzhokhar Tsarnaev, the suspect in federal custody for the Boston Marathon bombing, should be considered an enemy combatant only for interrogation purposes, not so he can be tried in a military tribunal, Sen. Lindsey Graham said Sunday.
"He is not eligible for military commission trial," the Republican senator from South Carolina said on CNN's "State of the Union." Graham argued Tsarnaev should be tried in a civilian trial in federal courts.
Graham was among Republicans Saturday who called for the U.S. government to label Tsarnaev as an enemy combat so authorities could waive his legal rights while they question him for intelligence purposes.
"Most Americans want to find out what he knew, who he associated with, does he know about terrorist organizations within or without the country that are trying to hurt us? Does he know about a future attack?" Graham said on Sunday.
Graham said none of that information could be used against him in civilian court. Anytime Tsarnaev is questioned "about his guilt or innocence," then "he's entitled to his Miranda Rights and a lawyer."
Critics have argued that because Tsarnaev is a naturalized citizen and authorities have so far found no links between him and terrorist organizations, he should not be tried as an enemy combatant. Foreigners with that designation have been held and tried in military trials at Guantanamo Bay.
But Graham said a U.S. citizen can be an enemy combatant and still be tried in civilian courts.
Tsarnaev had not been read his Miranda rights as of Saturday, and federal officials have not since said that he has. Miranda rights include the right to remain silent, the right to an attorney regardless of financial circumstances and the warning that any statements can be used to aid his prosecution.
Tsarnaev is currently hospitalized in "serious condition," according to Beth Israel Deaconess Medical Center.
A Justice Department official said federal prosecutors would use the public safety exception to the Miranda rule for Tsarnaev, which alloeditws investigators to question a suspect before apprising him of his rights when they believe there is an imminent public safety threat.
Federal officials called in the interagency High Value Detainee Interrogation Group, which includes investigators from the FBI and CIA who specialize in collecting intelligence from terrorism suspects, to question Tsarnaev.
But Graham and other Republicans argue the public safety exemption can only be applied 48 hours after arrest, and the "enemy combatant" label could extend that exemption for a longer period of time.
It's not clear, however, how long the public safety exemption could be used. Attorney General Eric Holder wrote in a 2010 memo the FBI believed "that in light of the magnitude and complexity of the threat often posed by terrorist organizations, particularly international terrorist organizations, and the nature of their attacks, the circumstances surrounding an arrest of an operational terrorist may warrant significantly more extensive public safety interrogation than would be permissible in an ordinary criminal case."
In recent examples of domestic terrorism handled by the Obama administration, individuals initially questioned under the public safety exemption were later tried in civilian court - Umar Farouk Abdulmutallab, the "underwear bomber" who attempted to blow up a Detroit-bound airliner on Christmas Day in 2009, and Faisal Shahzad for his 2010 attempt to detonate a bomb in Times Square.