Reports from Boston say the seriously injured surviving suspect in the bombings of the city's marathon has a gunshot wound to his throat and may never be able to give spoken testimony.
Investigators want to know what motivated Dzhokhar Tsarnaev and his brother Tamerlan to carry out the attacks, while Police Commissioner Edward Davis said he believed the pair had been planning more.
Two women and an eight-year-old boy were killed and about 180 injured in two blasts close to the finish line of the marathon on 15 April.
A top interrogation group is waiting to question Dzhokhar Tsarnaev, who is in a serious condition at a Boston hospital under armed guard after being arrested on Friday night. He was found badly injured and hiding inside a boat in a suburban backyard, the BBC reports.
The 19-year-old is heavily sedated and has a breathing tube in his throat. Tamerlan Tsarnaev, 26, died during a gunfight with police on Thursday night.
Police Commissioner Davis said the brothers had enough firepower and unused explosives to attack other targets. He said the pair had been carrying home-made bombs and grenades which they threw at police when cornered last week.
Mr Davis told a CBS news programme: "We have reason to believe, based upon the evidence that was found at that scene - the explosions, the explosive ordnance that was unexploded and the firepower that they had - that they were going to attack other individuals. That's my personal belief at this time."
He said more than 250 rounds of expended ammunition were found at the scene, and that the ground was "littered with unexploded improvised explosive devices that we had to point out to the arriving officers".
Officials are trying to trace all the weapons used by the brothers, Mr Davis said, adding that this would be a "significant part of the investigation".
A police officer was killed and a transport officer shot in the thigh during the operation to track down the brothers. Doctors treating the wounded officer, Richard Donohue, said on Sunday that he was in a stable but critical condition.