With one suspect dead and the other captured and lying grievously wounded in a hospital, the investigation into the Boston Marathon bombings turned on Saturday to questions about the men’s motives, and to the significance of a trip by one of the bombers took to Chechnya.Tamerlan Tsarnaev, who was killed early Friday after a shootout with police in Watertown, Mass., traveled to Russia for six months in 2012. Law enforcement officials are now conducting a review of that trip to see if Mr. Tsarnaev might have met with extremists or received training from them while abroad, current and former intelligence and law enforcement officials said.
Kevin R. Brock, a former senior F.B.I. 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. Monday had brought the bombing, near the finish line of the Boston Marathon, which killed three and wounded scores, and the tense days that followed culminated in Friday’s lockdown of the entire region as police searched for Mr. Tsarnaev’s younger brother from suburban backyards to an Amtrak train bound for New York City.
On Saturday morning, federal prosecutors were drafting a criminal complaint against Mr. Tsarnaev’s brother and suspected accomplice in the bombings, Dzhokhar A. Tsarnaev, 19, who was wounded in the leg and neck and had lost a great deal of blood when he was captured Friday evening. The F.B.I. and local law enforcement agencies continued to gather evidence and investigate the bombings, the slaying of a Massachusetts Institute of Technology police officer Thursday night and the subsequent battle with the police that left another officer critically wounded.
An official said the criminal complaint would 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.
President Obama and Republican lawmakers devoted their weekly broadcast addresses to the Boston attack, with both sides finding a common voice over the five days of uproar and lockdown leading up to the death of the elder Mr. Tsarnaev, an amateur boxer who seemed to follow a path of anger and alienation, and the capture of his seemingly more easygoing and Americanized brother.
In his weekly address, the president applauded the “heroism and kindness” on display in the aftermath of the bombings. “Americans refuse to be terrorized,” he said. “Ultimately, that’s what we’ll remember from this week.”
In the Republican response, Senator Tim Scott of South Carolina sounded a note of national unity. While the bombers hoped to “shake the confidence of a city,” he said, “they have instead only strengthened the resolve of our nation.”
The seeds of arguments to come were already apparent, however. Questions arose concerning the arrest and prosecution of the surviving brother, and whether he should be given a Miranda warning and other elements of constitutional rights in criminal cases. Further attention surrounds the government’s early scrutiny of Tamerlan Tsarnaev and whether warning signs may have been missed.
In the hours after the arrest, Senators Lindsey Graham of South Carolina and John McCain of Arizona, both Republicans, issued a statement late Friday calling for Dzhokhar Tsarnaev, who is a naturalized American citizen, to be treated like a terrorist, not a criminal, with reduced constitutional rights and no right to remain silent as promised in Miranda warnings.
