WASHINGTON -- With one suspect dead and the other captured and lying grievously wounded in a hospital, the investigation into the Boston Marathon bombings turned Saturday to questions about the men's motives and to the significance of an overseas trip one of them took last year.
Federal investigators are hurrying to review a visit that one of the suspected bombers made to Chechnya and Dagestan, predominantly Muslim republics in the north Caucasus region of Russia. Both have active militant separatist movements. Members of Congress expressed concern about the FBI's handling of a request from Russia before the trip to examine the man's possible links to extremist groups in the region.
Tamerlan Tsarnaev, who died early Friday after a shootout with police in Watertown, Mass., spent six months in Dagestan in 2012, and analysts said, that sojourn may have marked a crucial step in his path toward the bombings.
Kevin R. Brock, a former senior FBI and counterterrorism official, said, "It's a key thread for investigators and the intelligence community to pull on."
The investigators began scrutinizing the events in the months and years before the fatal attack as Boston began to feel like itself for the first time in nearly a week.
On Monday, the bombing near the finish line of the Boston Marathon killed three and wounded more than 170. The tense days that followed culminated in Friday's lockdown of the entire region as the police searched for Tsarnaev's younger brother from suburban back yards to an Amtrak train bound for New York City.
Dzhokhar Tsarnaev, 19, was taken into custody Friday night after he was found, bloody and weakened, hiding on a boat in a driveway in Watertown. He was still too wounded to speak Saturday, said Gov. Deval Patrick of Massachusetts.
Special counterterrorism agents trained in interrogating high-value detainees were waiting to question him, according to a law enforcement official. Questions arose about the administration's decision to question him for a period without giving him a Miranda warning under an exception for questions about immediate threats to public safety.
The brothers' motives are still unclear. Of Chechen heritage, they had lived in the United States for years, according to friends and relatives, and no direct ties have been publicly established with known Chechen terrorist or separatist groups. While Dzhokhar became a naturalized American citizen last year, Tamerlan was still seeking citizenship. Their father, Anzor, said Tamerlan had made last year's trip to renew his Russian passport.
The significance of the trip was magnified late Friday when the FBI disclosed in a statement that in 2011 "a foreign government" -- now acknowledged by officials to be Russia -- asked for information about Tamerlan. The request was "based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country's region to join unspecified underground groups."
The senior law enforcement official said the Russians feared he could be a risk, and "they had something on him and were concerned about him and him traveling to their region." Chechen extremists pose a greater threat to Russia than they do to the United States, counterterrorism specialists say, though some of the groups have had ties to al-Qaida. But the FBI never followed up on Tamerlan Tsarnaev once he returned, a senior law enforcement official acknowledged on Saturday, adding that its investigation did not turn up anything and it did not have the legal authority to keep tabs on him.
President Barack Obama and Republican lawmakers devoted their weekly broadcast addresses to the Boston attack, with both sides finding a common voice. Obama also met with his national security team for an update on the investigation.
"Americans refuse to be terrorized," Obama said. "Ultimately, that's what we'll remember from this week."
Since 1994, Russia and the U.S. have routinely exchanged requests for background information on residents traveling between the two countries on visa, criminal or terrorism issues. The FBI responded to the request by checking "U.S. government databases and other information to look for such things as derogatory telephone communications, possible use of online sites associated with the promotion of radical activity, associations with other persons of interest, travel history and plans, and education history," it said in a statement.
In January 2011, two agents from the bureau's Boston field office interviewed Tamerlan and family members, a senior law enforcement official said Saturday. According to the FBI's statement, "The FBI did not find any terrorism activity, domestic or foreign," and conveyed those findings to "the foreign government" by summer 2011.
Federal officials said Saturday that the Department of Homeland Security, however, had decided not to grant a petition from Tamerlan for U.S. citizenship after officials had found a record in his files that he had been interviewed by the FBI. His petition was held for further review. As the law enforcement official put it, "We didn't find anything on him that was derogatory."
The Russian state news agency RIA Novosti quoted the father of the Tsarnaev brothers recalling the FBI's close questioning of his elder son, "two or three times."
He said they had told his son that the questioning "is prophylactic so that no one sets off bombs on the streets of Boston."
In an interview in Russia, Zubeidat Tsarnaeva, the mother of the two men, said that the agents had told her that Tamerlan was "an excellent boy," but "at the same time, they told me he is getting information from really extremist sites, and they are afraid of him."
After the visit to Dagestan and Chechnya, signs of alienation emerged. One month after Tamerlan returned to the U.S., a YouTube page that appeared to belong to him was created and featured multiple jihadist videos that he had endorsed in the past six months.
The Boston bombings have led to increased cooperation between Washington and Moscow, a jarring shift coming amid weeks of rancor over American criticism of Russia's human rights record. Obama and Russian President Vladimir Putin spoke by telephone late Friday night, in a conversation initiated by the Russian side, the Kremlin announced. The Kremlin's statement said both leaders expressed "the building of close coordination between Russian and American intelligence services in the battle with global terrorism."
Nevertheless, there were glaring questions about the case, among them how Tamerlan had escaped attention after 2011.
A Russian intelligence official told the Interfax news service Saturday that Russia had not been able to provide the United States with "operatively significant" information about the Tsarnaev brothers "because the Tsarnaev brothers had not been living in Russia."
Andrei Soldatov, an investigative journalist who specializes in Russia's security services, said he believes that Tamerlan may have attracted the attention of Russian intelligence because of the video clips he had posted under his own name starting in 2010, which were included on a list of banned materials by the Federal Security Service.
On Saturday morning, federal prosecutors were drafting a criminal complaint against Dzhokhar Tsarnaev, who was wounded in the leg and neck.
An official said the criminal complaint would most likely include a constellation of charges stemming from both the bombings and the shooting, possibly including the use of weapons of mass destruction, an applicable charge for the detonation of a bomb. That charge, the official said, carries a maximum penalty of death. While Massachusetts has outlawed the death penalty, federal law allows it.
By ERIC SCHMITT, ELLEN BARRY, and MICHAEL S. SCHMIDT
The New York Times