The suspects, Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev, 19, came to the U.S. from Russia about a decade ago as ethnic Chechen refugees and were granted asylum, law enforcement sources have said. Tamerlan, who was killed in a gun battle with police Thursday, was a legal permanent U.S. resident. Dzhokhar, captured Friday, became a citizen on Sept. 11, 2012.
"This guy is probably not a Chechen separatist . . . I suspect he wasn't recruited by al-Qaida," said one senior counter terrorism official regularly briefed on the investigation, referring to Tamerlan, who traveled to Russia last year.
Rep. Peter King, R-N.Y., chairman of the intelligence subcommittee of the House Homeland Security Committee, agreed. "I don't think this was directed from overseas, I don't think this was planned from overseas."
Tamerlan Tsarnaev appears to have embraced Islamic extremism, the law enforcement official said, though it's unclear to what extent that was a main trigger for the violence.
King said it was possible Tamerlan met with extremists or received some training during a six-month trip to Russia in 2012, which officials are investigating.
But, the senior official said, the emerging story of the Tsarnaev brothers more likely fits the profile of previous domestic terror attacks and a number of mass shooting events in recent history, specifically noting "very striking" similarities between the Boston attack and the killing rampage of Anders Behring Breivik, the Norwegian right-wing extremist who killed 77 people in 2011.
In confrontations with the brothers Thursday and Friday, police faced a heavy arsenal of weapons.
One firearm was recovered after the shootout with police Thursday night in Watertown, where some 200 rounds of ammunition were exchanged, said the law enforcement official, who spoke on condition of anonymity because the case is still evolving.
That gun battle followed the shooting of a Massachusetts Institute of Technology police officer on campus.
Two more firearms were recovered in the backyard boat where Dzhokhar was captured Friday, the official said, adding that the serial identification on at least one of them "was ground down" to obscure the numbers.
He said that authorities consider the older brother to be the leader of the duo. "The brother was the catalyst in this thing," he said. "The younger brother followed him."
During an interview with CNN Saturday, Watertown Police Chief Edward Deveau said that the Thursday gun battle erupted when one of his officers spotted the brothers in two different cars. As he called for backup, the brothers exited the vehicles and "unloaded on our officers," Deveau said. "He was under direct fire . . . . He has to jam it in reverse and try to get himself a little distance."
"They had pipe bombs and explosives," Deveau said. "During the exchange, all of a sudden something gets thrown at police officers. We find out it was the exact bomb used in the marathon . . . a pressure cooker."
Ultimately, only one of the six officers was injured in the firefight.
"I'm extremely proud of these officers," Deveau said. "It was talent, guts and glory."
After Dzhokar's capture Friday evening, authorities decided not to read him his Miranda rights against self-incrimination, and hold him under a so-called public safety exception to the law, a move that has quickly raised legal and national security questions.
In 2011, a Justice Department memo expanded the use of the public safety exception in domestic terrorism cases, so that it can be invoked in exceptional circumstances even when there is not an imminent safety threat.
The changes were made after a controversy over the handling of the suspect in the Christmas Day 2009 airline bomb attempt, Umar Farouk Abdulmutallab, who was questioned by FBI agents for less than an hour before being read his rights.
A group of Republican lawmakers urged Saturday that wounded Dzhokhar Tsarnaev be treated as an enemy combatant and not a criminal suspect.
"A decision to not read Miranda rights to the suspect was sound and in our national security interests," the statement read. "However, we have concerns that limiting this investigation to 48 hours and exclusively relying on the public safety exception to Miranda, could very well be a national security mistake. It could severely limit our ability to gather critical information about future attacks from this suspect."
"The accused perpetrators of these acts were not common criminals attempting to profit from a criminal enterprise, but terrorists trying to injure, maim, and kill innocent Americans, read a statement issued by Sens. Lindsey Graham, R-S.C., John McCain, R-Ariz., and others.
The American Civil Liberties Union, meanwhile, said in a statement that "every criminal defendant" is entitled to Miranda rights, noting that Tsarnaev became a naturalized American citizen.
"The public safety exception should be read narrowly. It applies only when there is a continued threat to public safety and is not an open-ended exception to the Miranda rule," the ACLU said. "Every criminal defendant has a right to be brought before a judge and to have access to counsel. We must not waver from our tried and true justice system, even in the most difficult of times. Denial of rights is un-American and will only make it harder to obtain fair convictions."
Residents throughout greater Boston expressed relief Saturday and turned their focus to the first Red Sox home game since the bombings. Players were expected to swap their traditional white home uniforms for new ones with "Boston" written across the front.
In Boston Common on Saturday morning, about 20 police officers in fatigues assembled as part of a regional response team. They have been working 24-hour shifts since Monday, and participated in the extensive search and final showdown in Watertown on Friday.
They remained on standby due to the Red Sox game, a Bruins hockey match and other events, said logistics commander Jack Richman.
Richman, 56, a sergeant from Milton, Mass., was amazed at the gratitude of Bostonians. Earlier in the morning, when he and a few other officers stopped for breakfast at Mul's in South Boston, an anonymous benefactor picked up the tab.
"They've been overly thankful. It's overwhelming, the response from people," Richman said as he stood near the cluster of officers who smiled as a little boy passed and waved.
Richman's own feelings were mixed. There was joy, but also sorrow for the lives lost, including a fellow officer.
"It's like you just won the Super Bowl, but you still have to think about the casualties," he said.
Similar sentiments were shared hours earlier when dozens of people gathered in drizzle to light candles and leave written messages at a Boylston Street police barricade that has been transformed into a makeshift Boston Marathon memorial.
"THE EVIL ARE FEW. THE GOOD ARE MANY. GOOD WINS EVERY TIME," read one note amid a growing pile of flowers, stuffed animals and candles. "YOU MESSED WITH THE WRONG CITY!" read another.
"We feel violated more than anything," said Lindsay McNealy, who visited the shrine with her fiance, Dennis Riordan. "It's kind of like having someone ruin your birthday," she said of the attack.
The couple has never run in the marathon, but said they agreed to participate next year.
"I think everyone in Massachusetts should pick up and run at least a mile of it," Riordan said.
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