Despite a serious throat wound preventing him from speaking, the surviving Boston Marathon bombing suspect is beginning to respond to questions from investigators, federal officials tell NBC News.
Nearly 48 hours after he was taken into custody following an intense gun battle and manhunt, Dzhokhar Tsarnaev, 19, was communicating with a special team of federal investigators at Beth Israel Deaconess Hospital. He was responding to questions mostly in writing because of the throat wound, according to the officials, who spoke on condition of anonymity. The suspect remains in serious condition.
The throat wound may be the result of a suicide attempt, investigators said.
Officials are hoping to glean more information about the twin blasts Monday at the finish line of the Boston Marathon, which killed three people and injured more than 170, and determine whether Tsarnaev and his older brother, Tamerlan, who was killed in a firefight with police after a wild chase into the Boston suburb of Watertown on Thursday night, received assistance from others.
Word that the wounded suspect is able to communicate with authorities came as a surprise, especially after details about the severity of his injuries began to emerge earlier in the day.
Boston Mayor Thomas Menino told an interviewer that "we don't know if we'll ever be able to question the individual."
Law enforcement sources had said earlier they were putting the final touches on charges against Tsarnaev and would announce them Sunday. However, Justice Department officials said late in the day that charges would not be announced until Monday at the earliest. They did not give a reason for the delay.
Authorities have told NBC News that a special high value detainee interrogation team will question Tsarnaev without advising him of his Miranda rights. A "public safety exemption" allows investigators to question a suspect without being informed of his right to remain silent and to have an attorney present during questioning when it is thought that he or she might have vital information about a threat to public safety.
Other details on the Tsarnaevs emerged Sunday.
NBC News contacted the driver of an SUV who allegedly was carjacked by the brothers hours before the shootout. The driver, who asked that his identity not be revealed, said he escaped after the brothers drove his car to a gas station in Watertown. He described them as "brutal and cautious."
Also on Sunday, Massachusetts Gov. Deval Patrick said that surveillance video clearly puts Tsarnaev at the scene of the attack, acting suspiciously.
"It does seem to be pretty clear that this suspect took the backpack off, put it down, did not react when the first explosion went off and then moved away from the backpack in time for the second explosion," Patrick said on "Meet the Press." "It's pretty clear about his involvement and pretty chilling, frankly."
Patrick noted that while he had not personally viewed the video recordings, he was briefed by law enforcement on their contents.
More details about the Thursday night chase surfaced over the weekend.
The brothers hurled a pressure-cooker bomb similar to the two that went off at the marathon during the firefight, Watertown Police Chief Edward Deveau said on Saturday. The men were in two cars when confronted by a lone police officer, Deveau said, and later threw four grenade-like explosives at pursuing officers.
Still, much remained unknown on Sunday about what might have driven the two suspects to violence. The chairman of the House Intelligence Committee said on "Meet the Press" that Tamerlan may have traveled under an alias when he took a trip to Russia in 2012.
That trip may have been when Tamerlan, who the FBI identified as Suspect 1, "got that final radicalization to push him to commit acts of violence and where he may have received training," said committee chair Rep. Mike Rogers, R-Mich.
Also, crime scene units returned to the scene of Monday's twin explosions that brought an annual springtime rite to an end in screams and smoke. Debris and trash not far from the bomb site on Boylston Street were taken away in garbage trucks on Sunday after being sifted for evidence.
Secretary of Defense Chuck Hagel said Sunday he has not seen evidence to link the bombings to any militant or terrorist group, and declined to speculate on whether or not Tsarnaev could be sent to Guantanamo Bay.
"We just don't have the facts, and until we get the facts, then it will be the responsibility of law enforcement, DOJ, and other institutions to make some determination as to how that individual should be treated, detained, charged, and all that goes with it," Hagel said. "But right now we just don't know enough about it."
Investigators are taking a look at Tsarnaev's behavior after he returned to the campus of the University of Massachusetts at Dartmouth after the Monday bombings, Gov. Patrick said Sunday on "Meet the Press."
"There is evidence of some frankly kind of normal student behavior in those ensuing days, which when you consider the enormity of what he was responsible for certainly raises a lot of questions in my mind and as I say more to the point in the minds of law enforcement as well," Patrick said. "Those are the kinds of leads that still have to be pursued and run to ground."
In Boston, the hunt for the suspected perpetrators gave way to a time to mourn a week after the attacks. A funeral for marathon victim Krystle Campbell, 29, a restaurant manager, is scheduled for Monday at St. Joseph Church in her home town of Medford, Mass.
Menino and Patrick along with the central charitable One Fund Boston called for a minute of silence at 2:50 p.m. Monday to mark a week since the bombings. Bells will ring throughout the city and Massachusetts after the minute's passage, according to a statement from the mayor's office.
One person injured in the marathon blast was released from the hospital on Sunday, though 52 are still receiving treatment in Boston hospitals, with three in critical condition.
About 36,000 runners participated in the London Marathon on Sunday amid heightened security, many of them wearing black ribbons to commemorate the victims in Boston or carrying "For Boston" signs.