(CNN) -- Dzhokar Tsarnaev, the surviving suspect in the Boston Marathon bombings, may be charged in his hospital bed Sunday, a Department of Justice official told CNN.
Because Tsarnaev is still in serious condition, a judge would come to his hospital bedside to charge him, a law enforcement source said, noting that suspects who face federal charges are normally arraigned within 48 hours of arrest. Tsarnaev is currently unable to speak.
Authorities have not said publicly what charges will be filed.
A Justice Department official, speaking on condition of anonymity, told CNN he will face federal terrorism charges and possibly state murder charges.
Although Massachusetts does not have the death penalty, prosecutors could seek the death penalty at the federal level, the Justice Department official said.
Lawmaker believes slain suspect trained in Russia
New details emerged Sunday as investigators tried to determine more about the brothers they believe were behind attacks last week that killed three spectators and a police officer.
House Homeland Security Chairman Michael McCaul told CNN that slain suspect Tamerlan Tsarnaev, Dzhokar Tsarnaev's older brother, received training while he was in Russia for six months in 2012.
The Texas Republican also questioned why the FBI did not take further action against Tsarnaev when he was investigated before his trip.
Tsarnaev may have traveled under an alias when he went to Russia, House Intelligence Committee Chairman Rep. Mike Rogers said on CNN's "State of the Union."
Rogers, a Republican from Michigan, also told NBC that Tamerlan Tsarnaev may have become radicalized by Islamic extremists during that trip.
The Russian embassy tweeted Friday that the brothers were not on the consular registry at the embassy in Washington nor the general consulate in New York.
Dzhokar Tsarnaev remains under heavy guard. His brother was killed early Friday as the pair tried to elude police.
The brother: Hints of radicalization
The Tsarnaev family hails from the Russian republic of Chechnya and fled the brutal wars there in the 1990s. The two brothers were born in Kyrgyzstan.
An FBI official said Saturday agents interviewed Tamerlan Tsarnaev in 2011 at the request of the Russian government. The FBI said Russia claimed he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010.
Tamerlan Tsarnaev apparently became increasingly radical in the last three or four years, according to an analysis of his social media accounts and the accounts of family members. But so far, there is no evidence of active association with international jihadist groups.
In August 2012, soon after returning from a long visit to Russia, the older Tsarnaev created a YouTube channel with links to a number of videos.
Two videos under a category labeled "Terrorists" were deleted. It's not clear when or by whom.
But analysis by CNN and the SITE Intelligence Institute has uncovered a screen grab from one of those videos. It features members of the group Imarat Kavkaz, identifiable by the logo on their shirts. Imarat Kavkaz is the most potent militant Islamist group in the north Caucasus region, which includes Chechnya and Dagestan.
Separately, a U.S. intelligence source told CNN that investigators are looking into whether Tsarnaev had any connections with the group, known in English as Caucus Emirates. The source says Tsarnaev had several computer links to the group in his social media activities, and investigators are looking into the possibility that he received "operational plans" from this group.
Imarat Kavkaz has its roots in the 1990s Chechen insurgency. It was founded in 2007 to bring together various jihadist groups fighting to create an Islamic state in the region.
Its overall leader is Doku Umarov, a veteran Chechen guerrilla who claimed responsibility for the 2011 bombing of Moscow's international airport.
Rebels who call themselves Mujahideen of the Caucasus Emirate Province of Dagestan issued a statement Sunday, saying they are not fighting the United States.
"We are at war with Russia," it said. The statement also said that children are never targets of the group.
So far, evidence suggests that the two brothers acted alone in the bombings and subsequent shootout, Deveau told CNN on Saturday.
"From what I know right now, these two acted together and alone," the police chief said. "I think we have to be ever vigilant, and we're learning as we go along, but as far as this little cell -- this little group -- I think we got our guys."
What's next for the suspect?
Authorities have not publicly detailed how Tsarnaev was injured, but a federal official said the 19-year-old has injuries to the throat.
An official who has been briefed on the case said he was "intubated and sedated."
The government has invoked the public safety exception, a designation that allows investigators to question Tsarnaev without reading him his Miranda rights and without a lawyer present,
said another Justice Department official, also speaking on condition of anonymity.
Secretary of Defense Chuck Hagel told reporters on a flight to Israel that the attack was "criminal," adding that "every region of the world is not safe from these terrible acts."
He also said he has not seen any intelligence that linked the brothers to any terrorist organization, but it was still early in the investigation.
"I, and I think all of the law enforcement professionals, are hoping for a host of reasons that the suspect survives, because we have a million questions, and those questions need to be answered," Massacusetts Gov. Deval Patrick said Saturday.
The chief of police where Tsarnaev was captured said officers did not question the suspect immediately after he was found.
"There was no interviewing at the scene. He needed aid, and we got him to the hospital," Watertown Police Chief Edward Deveau said.
After the bombings, Tsarnaev went out to party
As an army of officers hunted for the suspects in Monday's marathon bombings, Tsarnaev acted like any other college sophomore.
He was on the campus of University of Massachusetts-Dartmouth every day after the attack until late Thursday, a university official told CNN. Tsarnaev attended classes and dorm parties while much of Boston was at a tense standstill.
A student at the school told The Boston Globe she saw Tsarnaev on Wednesday night at a party that was attended by some of his friends from intramural soccer.
"He was just relaxed," she said, asking the paper not to print her name.
At the dorm where Tsarnaev lived, students joked Thursday as they viewed the FBI photos on television, a senior who lived in the suspect's dorm told The Boston Globe.
"We made a joke like, that could be Dzhokar," Pamala Rolon said. "But then we thought it just couldn't be him. Dzhokar? Never."
The campus, which was closed during the search for the bombing suspects, reopened Sunday morning.
A stolen Mercedes
Soon after the FBI released the suspects' photos to the public, the brothers killed a Massachusetts Institute of Technology police officer for no obvious reason, officials said. The Tsarnaevs then hijacked a Mercedes, telling the driver they were the marathon bombers, and hurled explosives at the pursuing officers, authorities said.
Handguns, a rifle and at least six bombs -- three of which exploded -- were found at the scene, Deveau told CNN's Wolf Blitzer.
"They jump out of the car and unload on our police officer," Deveau said "They both came out shooting -- shooting guns, handguns. He's under direct fire, very close by."
The Watertown police chief estimated there were more than "200 shots fired in a five- to 10-minute period."
Tamerlan Tsarnaev ran out of ammunition during the shootout and was tackled by officers. That's when the younger Tsarnaev drove the Mercedes toward the officers and his brother.
"They dive out of the way, and he (the younger brother) drives over his brother and drags him a short distance down the street," Deveau said.
Tamerlan Tsarnaev was later pronounced dead at a hospital. He was wearing explosives and a triggering device when he died, a source briefed on the investigation told CNN.
One of the brothers threw an explosive at the officers. Investigators later discovered it was a pressure cooker bomb, similar to the ones used at the marathon Monday, Deveau said.
CNN's Tim Lister, Paul Cruickshank, Deborah Feyerick, Jill Dougherty, Pamela Brown, Julian Cummings, Barbara Starr, Ann O'Neill, Melissa Gray, Susan Candiotti, Tom Watkins, Jake Tapper, Shannon Travis and Drew Griffin contributed to this report.
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