Heated debate over Boston suspect Courtney Brillant helps her two-year-old son Wesley to place a flower at a memorial for the victims of the Boston marathon bombings Investigators are waiting to question the surviving suspect in the Boston marathon bombings, Dzhokhar Tsarnaev, amid intensifying debate in the US about how the 19-year old should be tried once police lay charges. The Federal Bureau of Investigation is also coming under pressure after its admission that it had interviewed his now deceased elder brother, Tamerlan Tsarnaev, in 2011, after Russia raised concern that he might have terror links. Mr Tsarnaev remained in a serious condition on Sunday at Boston's Beth Israel Deaconess Medical Centre. While Massachusetts does not have the death penalty, he could face execution if found guilty of federal terrorism charges for the April 15 bombings that killed three people and maimed many others. "I hope that the US attorney takes him on the federal side and throws the book at him," Thomas Menino, Boston mayor, told ABC's This Week. Mr Menino said he didn't know if the authorities will ever be able to question the suspect. The Obama administration has already said that it will use the so-called "public safety" provision to allow Mr Tsarnaev to be questioned initially without a lawyer present and without his rights being read to him. A suspect's Miranda rights can be suspended when there is an imminent threat to public safety, for example, to find out where a gun is hidden or a bomb has been placed. Anthony Romero, executive director of the American Civil Liberties Union, said in a statement that the public safety exception "should be read narrowly." "It applies only when there is a continued threat to public safety and is not open-ended - every criminal defendant has a right to be brought before a judge and to have access to counsel," he said. Two senior Republican senators, Lindsey Graham and John McCain, have already called for him to be treated even more harshly and to be tried as an enemy combatant by a military tribunal. Their approach received backing from former New York mayor Rudy Giuliani, who told CBS on Sunday the authorities should dispense with "political correctness" and treat the suspect as a terrorist. "These two young men joined a war and they are at war against us," he said. The FBI said in a statement that it had found no "terrorism activity, domestic or foreign" after it had interviewed Tamerlan Tsarnaev and family members in 2011. "I don't know if our laws are insufficient or the FBI failed, but we're at war with radical Islamists and we need to up our game," Mr Graham told CNN. Ed Davis, Boston police commissioner, said on Sunday that the 250 rounds of ammunition, explosive devices and homemade grenades found in the brothers" possession suggested they "were going to attack other individuals."