The surviving Boston bombings suspect is recovering in hospital with serious injuries, as investigators seek a motive for the attacks and try to determine whether the brothers accused of the crime acted alone.
Dzhokhar Tsarnaev, 19, was captured late on Friday after a gunfight with police.
His apprehension in a Watertown backyard sent waves of relief and jubilation throughout Boston.
Tsarnaev's brother, Tamerlan, 26, died on Thursday after a shootout with police.
His younger brother was shot in the throat and could not speak because of injuries to his tongue, said a source close to the investigation.
Al Jazeera's Alan Fisher, reporting from Boston, said that when Tsarnaev was in a stable condition at Beth Israel Deaconess Medical Centre in Boston and remained after heavy police guard.
"We know he lost a lot of blood," Fisher said.
"We believe he suffered several gunshot wounds."
It was unclear when Tsarnaev would be able to talk again or when he would be charged.
Life in Boston began to return to normal on Saturday as the Red Sox returned to Fenway Park for the first time since the bombings, paying an emotional tribute to the victims and the first responders before their baseball game.
The London Marathon also held a memorial service for victims of the Boston bombings before the event and many of the 36,000 runners wore black armbands to remember the dead and wounded.
The issue in the US turned to what rights Tsarnaev should have, as Massachusetts governor Deval Patrick said "we have a million questions" to ask him.
"Those questions need to be answered," he said.
Fisher said several US senators believed Tsarnaev should be treated as an enemy combatant before he could be given his rights, which he has yet to be read.
But groups including the American Civil Liberties Union believed it was "un-American" for that to happen and that Tsarnaev must be treated properly so he could not appeal against a jail sentence if he was found guilty.
The brothers are suspected of setting off bombs made in pressure cookers and packed with ball bearings and nails at the crowded finish line of Monday's marathon, killing three people and injuring 176.
|Dzhokhar Tsarnaev was shot in the throat and could not speak because of injuries to his tongue, sources say [AFP]
The FBI believes Tamerlan was the leader of the pair, although investigators were checking on people who had contact with both brothers to see if anyone else was involved, said a senior US law enforcement source.
Early indications were that the brothers acted alone, Watertown Police Chief Edward Deveau told CNN on Saturday.
Parents say sons framed
The FBI said it interviewed Tamerlan in 2011 at the request of a foreign government - identified by a law enforcement source as Russia - after that country raised concerns that he followed radical Islam.
The FBI did not find any "terrorism activity".
Tamerlan travelled to Moscow in January last year and spent six months in the region, a law enforcement source said, but it was unclear what he did while he was there.
|Al Jazeera's David Chater reports from Dagestan's capital Makhachkala on Tsarnaev brothers roots
President Barack Obama said on Friday that questions remained from the bombings, including whether the two suspects received any help. Obama has described the bombings as an act of terrorism.
Tsarnaev was a student at the University of Massachusetts at Dartmouth and is believed to have been on the college campus on Tuesday, Wednesday and Thursday, a university official said.
The family emigrated to the United States about a decade ago. The brothers spent their early years in a small community of Chechens in the central Asian country of Kyrgyzstan, a mainly Muslim nation of 5.5 million.
They moved in 2001 to Dagestan, a southern Russian province that lies at the heart of a violent insurgency and where their parents now live.
In separate interviews, the parents of the Tsarnaev brothers said they believed their sons were incapable of carrying out the bombings.
"Somebody clearly framed them. I don't know who exactly framed them, but they did. They framed them. And they were so cowardly that they shot the boy dead," father Anzor Tsarnaev said in an interview with Reuters news agency in Dagestan's provincial capital, Makhachkala, clasping his head in despair.