Boston bombing: One week later, what do we know?

BOSTON, Mass. — It has been one week since two separate bombs ripped through cheering crowds at the Boston Marathon, killing three people and injuring at least 176 others. One suspect is in custody after a dramatic manhunt which forced the city of Boston into lockdown, and another died in a violent firefight.

People across the state of Massachusetts will observe a moment of silence at 2:50 p.m., the exact time one week ago that the first of the two bombs exploded near the marathon finish line.

Details have begun to emerge about the two suspects' lives and possible motivations, though many questions remain.

The surviving suspect, Dzhokhar Tsarnaev, was formally charged on Monday afternoon.

"There has been a sealed complaint filed," said Gary Wente, circuit executive for the US Courts for the First Circuit.

The Department of Justice said Dzhokhar has been charged with using a weapon of mass destruction and malicious destruction of property resulting in death. The charges mean he could face the death penalty.

White House spokesman Jay Carney said on Monday, Dzhokhar "will not be treated as an enemy combatant." Some Republican lawmakers, including Sens. Lindsey Graham, John McCain and Kelly Ayotte, had called for him to be treated as such.

GlobalPost analysis: Russia’s role in Tsarnaev investigation is unclear

Carney said however that Dzhokhar is a US citizen and should be tried in civilian court.

Investigators are looking into whether Tamerlan, Dzhokhar's 26-year-old brother who died in a firefight with police on Thursday night, had turned toward radical Islam, according to a detailed profile of the suspects by The Wall Street Journal.

"Once known as a quiet teenager who aspired to be a boxer, Tamerlan Tsarnaev delved deeply into religion in recent years at the urging of his mother, who feared he was slipping into a life of marijuana, girls and alcohol," The Journal wrote.

The Boston Globe uncovered how Tamerlan angrily disrupted talks at local mosques when their sermons clashed with what have been described as his increasingly radical beliefs. 

Officials are also interested in a six-month trip Tamerlan took last year to Dagestan, a republic bordering Chechnya.

Tamerlan's parents, Anzor and Zubeidat Tsarnaev, told the Associated Press that he spent the time visiting relatives, not meeting Islamist terrorists.

The brothers had spent their early years in the country of Kyrgyzstan, reportedly living in a small community of Chechens. They moved to Dagestan in 2001.

Rebels from the North Caucasus region issued a statement on Sunday saying they were not associated with the bombing. "The Caucasian Mujahedeen are not fighting with the United States of America," read the statement. "We are at war with Russia, which is responsible not only for the occupation of the Caucasus, but also for heinous crimes against Muslims."

Federal authorities have also sought to speak to Tamerlan's widow, Katherine Russell, who has been staying with her parents in North Kingstown, R.I., since he was killed.

Amato DeLuca, Russell's lawyer, said he was in talks with authorities on how to proceed. When he was asked about whether Russell noticed anything amiss in the days after the bombing, DeLuca told the AP, "Not as far as I know."

"He said she learned her husband was a suspect in the bombings by seeing it on TV."

Dzhokhar is in serious condition at Beth Israel Deaconess Hospital. It is not yet clear how Dzhokhar was wounded, though Boston Mayor Thomas Menino said Sunday that the teenager sustained wounds to the throat. Authorities think there is a possibility he tried to kill himself.

Sources told NPR that while wounds on his neck and jaw prevented him from talking, Tsarnaev was communicating through writing.

The following tweet is from the US Attorney's office of Massachusetts:

Investigators are eager to determine if the Tsarnaev brothers were working alone. Boston Police Commissioner Ed Davis and Mayor Menino both said they believed the brothers were operating on their own.

Davis said at least four more undetonated devices were discovered during their investigation, leading officials to believe the suspects had been planning more attacks.

Fear of additional attacks is the reason the Justice Department cited for invoking a "public safety exception" in not reading Dzhokhar his Miranda rights.

According to NBC, authorities recovered an "arsenal" of deadly weapons in the course of their investigation, including bombs, homemade grenades, guns and hundreds of rounds of ammunition.

The FBI, meanwhile, is broadening its investigation and pressing the Russian government for more details about a request from Russia in 2011 regarding Tamerlan's possible links to extremists, a senior US official told The New York Times.

US Attorney Carmen Ortiz was preparing criminal charges against Dzhokhar, which were filed on Monday.

Here is how the public marked the one-week anniversary: