BOSTON (Reuters) - With the surviving suspect in the Boston Marathon bombings lying seriously wounded in a hospital and unable to speak on Saturday, investigators worked to determine a motive and whether the ethnic Chechen brothers accused of the attack acted alone.
Dzhokhar Tsarnaev, 19, was captured late on Friday after a gunfight with police that ended a daylong manhunt and sent waves of relief and jubilation throughout Boston. His brother, Tamerlan, 26, died on Thursday after a shootout with police.
The younger brother was shot in the throat and could not speak because of injuries to his tongue, said a source close to the investigation. It was unclear when he would be able to talk again or when he would be charged.
"It's serious ... he's not yet able to speak," Massachusetts Governor Deval Patrick told reporters on Saturday. "We have a million questions and those questions need to be answered."
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.
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.
"When (Tsarnaev) was apprehended and we saw the reactions of everyone in Watertown, I just got online and got two tickets for the game," said Linda Gibbs, 52, from Westborough, Massachusetts. "We just really wanted to be here and to support everyone."
Tsarnaev had been hiding in a boat parked in the backyard of a house in the suburb of Watertown and was captured after a resident spotted blood on the boat and called police. He was being treated at Beth Israel Deaconess Medical Center in Boston.
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 U.S. law enforcement source.
Early indications are the brothers acted alone, Watertown Police Chief Edward Deveau told CNN on Saturday. "From what I know right now, these two acted together and alone," he said. "But as far as this little ... group, I think we got our guys."
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 traveled 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.
President Barack Obama said on Friday after the capture that questions remained from the bombings, including whether the two suspects received any help. Obama has described the bombings 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, said a university official, citing witnesses, swipe cards and security cameras.
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. The family moved in 2001 to Dagestan, a southern Russian province that lies at the heart of a violent Islamist 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. Others remembered the brothers as friendly and respectful youths who never stood out or caused alarm.
"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 in Dagestan's provincial capital, Makhachkala, clasping his head in despair.
Ruslan Tsarni, who said he was an uncle of the brothers, told CNN on Saturday he first noticed a change in Tamerlan Tsarnaev's religious views in 2009. He said the radicalization of his nephew happened "in the streets of Cambridge."
The bombings prompted contact between the United States and Russia on terrorism and the Kremlin said on Saturday that the presidents of both countries had agreed by telephone to increase cooperation on counterterrorism.
On Saturday, several Republican lawmakers called on Obama to try Tsarnaev as an "enemy combatant" under terms of war, without entitlement to Miranda rights - usually given by police to suspects before they are interrogated so statements can be admissible in court.
Authorities did not read the teenager the Miranda warning.
A Justice Department official said the government was invoking the public safety exception to Miranda to question the suspect extensively about other potential explosive devices or accomplices and to gain critical intelligence.
The Federal Public Defender Office said on Saturday it would represent Tsarnaev once charges were filed.
After combing through a mass of pictures and video from the site in the minutes before the Boston marathon bombing, the FBI publicized pictures of the two men on Thursday and asked the public for help in identifying them.
Just hours later, events began to unfold with the fatal shooting of a police officer on the campus of the Massachusetts Institute of Technology and finally the Watertown firefight, during which police say the brothers threw bombs at officers. Tamerlan suffered fatal wounds, while Dzhokhar escaped on foot.
The hunt for Tsarnaev emptied Boston's streets as the city went into lockdown for most of Friday. Public transportation was suspended and air space restricted. Famous universities, including Harvard and MIT, closed after police told residents to remain at home.
Additional reporting by Martinne Geller, Tabassum Zakaria, Mark Hosenball, John Shiffman, Jim Bourg, Svea Herbst-Bayliss, Daniel Lovering, Ben Berkowitz, Barbara Goldberg, Ed Krudy and Olga Dzyubenko; Writing by Michelle Nichols; Editing by Doina Chiacu, Vicki Allen and Peter Cooney