As authorities wait to interrogate the surviving Boston Marathon bombing suspect in hospital, questions are being asked about whether authorities missed warning signs leading up to the attack.
Nineteen year old Dzhozkar Tsarnaev is in a serious condition, and is yet to be formally charged for the attack which killed three people and injured 170.
After one of the biggest manhunts in United States police history he was found hiding in a boat parked in the back yard of a Boston house and was detained after an exchange of fire with police.
His elder brother, Tamerlan Tsarnaev, was killed in a gun battle with police on Friday.
The ABC reports that the 26 year old had posted militant Islamic videos on social media sites, and was previously questioned by the FBI at the request of a foreign government.
He also made a six month trip to Russia's volatile Caucasus region last year.
The Republican senator Lindsey Graham said all that should have been a red flag.
"The ball was dropped. I don't know if our laws are insufficient or the FBI failed."
There are now calls for Dzhozkar Tsarnaev to be treated as an enemy combatant which would give him the same status as Guantanamo Bay, but others insist that as a naturalised American citizen he must be given a civilian criminal trial.
The Boston police commissioner says the brothers were "probably planning further attacks".
Ed Davis says they had been carrying homemade bombs and grenades that they threw at police when cornered on Friday.
A special interrogation team is waiting to speak to Dzhokhar Tsarnaev who is seriously injured in hospital.
The teenager, of Chechen origin, is being held under armed guard at the Beth Israel Memorial Hospital where many victims of the bombing are also being treated, the BBC reports.
Anti-terrorism officers want to establish whether he knows of any other threats and whether he and his brother were helped by anyone else.
Citing a public safety exception, officials have said they intend to question Dzhokhar Tsarnaev without reading him the standard statement informing suspects they have a right to a lawyer and to remain silent.
The decision has been criticised by the American Civil Liberties Union which said such an exemption applied only in the case of immediate threats, and should not be removed in an open-ended way.
But Boston's mayor Tom Menino said he did not know if it would be possible to ever question the bomb suspect, but he did not elaborate.
The extended family of the brothers have told the BBC that the elder brother was radicalised while he was in the United States.
Tamerlan's aunt said it was clear from long discussions he had with her husband, that he had converted to an extreme version of Islam which wasn't shared by the rest of the family.
Resident found Dzhokhar Tsarnaev seriously injured
Thousands of police swamped the streets of Boston on Friday, public transport was halted and people told to stay indoors in a manhunt that put the city in virtual lockdown.
The search began when a police officer was shot dead in the Cambridge area of Boston. Shortly afterwards a car was hijacked, then a gun battle began further west, in Watertown, injuring one police officer and fatally wounding Tamerlan Tsarnaev.
Police scoured the suburb and at about 7pm, an hour after lockdown orders were lifted, a gunfight broke out in Franklin Street.
It later emerged a resident had found seriously injured Dzhokhar Tsarnaev hiding in a boat in his backyard.
Police say attempts to negotiate with him failed, and he was arrested after an exchange of fire.
The FBI said it had intervewed him following a tip from a foreign government two years ago, and checks of travel records, internet activity and personal associations, "did not find any terrorism activity" at that time.
