BOSTON » Boston Marathon bombing suspect Dzhokhar Tsarnaev lay hospitalized under heavy guard today as people across the Boston area breathed easier and investigators tried to piece together the who and why of the deadly plot.

Tsarnaev, 19, was reported in serious condition and unable to be interrogated the morning after he was pulled, wounded and bloody, from a boat parked in a Watertown backyard. The capture came at the end of a tense day that began with his older brother, Tamerlan, dying in a desperate getaway attempt.

President Barack Obama said there are many unanswered questions about the Boston bombings, including whether the Tsarnaev brothers — ethnic Chechens from southern Russia who had been in the U.S. for about a decade and lived in the Boston area — had help from others. The president urged people not to rush judgment about their motivations.

U.S. officials said a special interrogation team for high-value suspects would question Tsarnaev without reading him his Miranda rights, invoking a rare public-safety exception that exists to protect police and the public from immediate danger.

The American Civil Liberties Union expressed concern about that possibility. Executive Director Anthony Romero said the exception applies only when there is a continued threat to public safety and is "not an open-ended exception" to the Miranda rule, which guarantees the right to remain silent and the right to an attorney.

Dzhokhar Tsarnaev’s capture touched off raucous celebrations in and around Boston, with chants of "USA! USA!" Residents flooded the streets in relief and jubilation four days after the twin explosions ripped through the marathon crowd at the finish line, killing three people and wounding more than 180.

The all-day manhunt Friday brought the Boston area to a near standstill and put people on edge across the metropolitan area.

The break came around nightfall when a homeowner in Watertown saw blood on his boat, pulled back the tarp and saw a bloody Dzhokhar Tsarnaev hiding inside, police said. After an exchange of gunfire, he was seized and taken away in an ambulance.

"They finally caught the jerk," said nurse Cindy Boyle of Watertown. "It was scary. It was tense."

During the long night of violence leading up to the capture, the Tsarnaev brothers killed an MIT police officer, severely wounded another lawman and took part in a furious gun battle and car chase in which they hurled explosives at police from a large homemade arsenal, authorities said.

Police said three other people were taken into custody for questioning at an off-campus housing complex at the University of Massachusetts Dartmouth where the younger man may have lived.

Chechnya, where the Tsarnaev family has roots, has been the scene of two wars between Russian forces and separatists since 1994. That spawned an Islamic insurgency that has carried out deadly bombings in Russia and the region, although not in the West.

The FBI said that a foreign government told the bureau in early 2011 about information that Tamerlan Tsarnaev was a follower of radical Islam.

According to the FBI, the foreign government said that based on its information, Tamerlan Tsarnaev was a strong believer and that he had changed drastically since 2010 as he prepared to leave the U.S. for travel to the country’s region to join unspecified underground groups.

The FBI said it interviewed Tsarnaev and relatives, and did not find any domestic or foreign terrorism activity.

Albrecht Ammon, a downstairs-apartment neighbor of Tamerlan Tsarnaev in Cambridge, said in an interview that the older brother had strong political views about the United States. Ammon quoted Tsarnaev as saying that the U.S. uses the Bible as "an excuse for invading other countries."

Tamerlan Tsarnaev had studied accounting as a part-time student at Bunker Hill Community College in Boston for three semesters from 2006 to 2008, the school said. He was married with a young daughter.

Dzhokhar Tsarnaev was a student at the University of Massachusetts Dartmouth. Students said he was on campus this week after the Boston Marathon bombing.

Sullivan and Associated Press writers Stephen Braun, Jack Gillum and Pete Yost reported from Washington. Associated Press writers Mike Hill, Katie Zezima, Pat Eaton-Robb and Steve LeBlanc in Boston, Rodrique Ngowi in Watertown, Mass., and Jeff Donn in Cambridge, Mass., contributed to this report.