Law enforcement sources told ABC News that Tsarnaev is awake and is sporadically answering questions in writing. The 19-year-old suspect remains in serious but stable condition, according to a statement by the FBI, who cited Beth Israel Deaconess Medical Center officials.
ABC News reports that Tsarnaev was wounded in the neck and throat area and is having difficulty speaking. He apparently knows that his brother has died. Investigators are trying to determine whether the brothers were part of a larger network.
Charges will likely be filed in the coming days against Tsarnaev. There was word a news conference would be held Sunday to announce the charges, but the conference was called off. It was not clear why.
Tsarnaev could face charges at the state and federal levels, and it is believed the charges will allow the federal government to pursue the death penalty. Massachusetts has no death penalty.
A moment of silence was scheduled to take place at 2:50 p.m. Monday in Massachusetts to mark the time the bombs went off just one week before. The moment of silence will be followed by the ringing of bells throughout Boston and the state. This comes after religious leaders headed an interfaith service Sunday morning at the same church President Barack Obama attended a service a few days before to honor bombing victims.
Tsarnaev was taken into custody on Friday after a massive manhunt that effectively shut down the city of Boston. Investigators found him hiding in a tarp-covered boat, which was parked in a home in Watertown, Mass.
Overnight, Massachusetts State Police released footage shot by a helicopter equipped with thermal imaging during the last minutes of the intense manhunt. The video shows a glowing white mass, which is Tsarnaev, huddled inside the boat. Later, the footage shows small explosions on the boat, believed to be flash-bang grenades used by police to stun and disorient the suspect.
Officials said FBI negotiators tried for 15 to 20 minutes to convince Tsarnaev to surrender. He eventually simply fell out of the boat.
Tsarnaev was pulled from the boat wounded and bloody. He was taken to Beth Israel Deaconess Medical Center, the same hospital where his brother, first bombing suspect 26-year-old Tamerlan Tsarnaev, died earlier the same day following a gun battle with police. Tsarnaev is under heavy guard.
The bombing at the finish line of Monday's Boston Marathon killed three, including a young boy, and wounded about 170 others. A Massachusetts Institute of Technology officer was allegedly killed by the Tsarnaev brothers Wednesday night, and a Boston transit officer was wounded in a subsequent shootout.
One focus of the investigation surrounds a six-month trip Tamerlan Tsarnaev took to the semi-autonomous Russian province of Dagestan, which has become a hotbed of militant Islamic activity, according to ABC News.
The FBI said it interviewed Tamerlan Tsarnaev at the request of Russian authorities, but their investigation, which included looking into phone records, Internet activity and associates, found he had no terror ties.
After Tamerlan Tsarnaev had been investigated, FBI officials said it had to stop monitoring him by law since they found nothing incriminating.
After a high-tension week, Boston is trying to move forward. Saturday marked the first Boston Red Sox game at Fenway Park since the bombing. The team's home jersey read "Boston" instead of "Red Sox." Singer Neil Diamond sang Fenway favorite, "Sweet Caroline."
A candlelight vigil was held Saturday night for Sean Collier, the slain MIT officer. A moment of silence is planned for Monday at 2:50 p.m. ET to mark exactly one week since the bombings.
In Southern California on Sunday, people showed their support for the bombing victims and the people of Boston. A fundraiser was held at Sonny McLean's Irish Pub in Santa Monica.
More than 500 people turned out to the event, which was organized by three Boston University alumni. Many who showed up were Massachusetts natives now living in the Southland.
The money raised was going to the Claddaugh Fund, which will help the victims of the deadly attack.
ABC News contributed to this report.