Doug Stanglin, USA TODAY

Dzhokhar Tsarnaev, the Boston Marathon bombing suspect, has told investigators that his brother was the driving force behind the attacks and that they were motivated by religion, but did not have help or contact from terrorists or groups overseas, according to media reports quoting U.S. officials.

Tsarnaev, who was arraigned in his hospital bed Monday on charges of using and conspiring to use a weapon of mass destruction resulting in death, has been questioned by interrogators.

CNN quotes an unidentified federal law enforcement official as saying that the 19-year-old suspect has indicated that no one else was involved in the attacks other than his now deceased brother, Tamerlan.

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His 26-year-old brother was killed during a shootout with Watertown police Thursday night and may have sustained fatal injuries when Dzhokhar ran over his body while making his escape in an SUV.

NBC News also reports that Dzhokhar, who has injuries in his throat and tongue, has responded to questions about the attack by writing down some answers or simply nodding.

Several officials familiar with the initial interrogation described Tsarnaev's behavior during questioning as cooperative, NBC reports.

NBC News, quoting an unidentified senior government official, also says Tsarnaev indicated that the two brothers conceived of the bombing attack on their own and were motivated by religious fervor. These officials also say that Tsarnaev told them they learned how to make bombs on the Internet.

Three people were killed and more than 170 injured when two bombs went off at the finish line to the Boston Marathon. Federal officials say that at least one of the homemade devices was a pressure cooker packed with metal and explosives.

Sean Collier, a police officer at MIT, was also killed during the five-day manhunt that ended with Dzhokhar's capture in Watertown on Friday night.

Vice President Biden is scheduled to travel to Massachusetts on Wednesday to attend a memorial service for the slain officer, according to a White House official source.

The heart of the criminal case against Tsarnaev is based on dramatic video and photographic evidence that prosecutors alleged Monday shows him placing a backpack believed to contain a powerful bomb at the exact site of the second explosion before calmly walking away.

A chilling frame-by-frame account, outlined in an 11-page criminal complaint unsealed Monday, offers the fullest description yet of the moments before two coordinated explosions rocked the iconic footrace, causing death, injury and mayhem.

U.S. Magistrate Marianne Bowler, convening a brief hearing at the suspect's bedside, advised Tsarnaev of his rights and the charges against him.

"The court is satisfied that the defendant is alert and able to respond to charges,'' the court clerk noted in a record of the proceeding.

The documents also contain a dramatic witness account from the victim of a late Thursday night carjacking in Cambridge, Mass. The victim, who was not identified in court records, alleged that one the Tsarnaev brothers - believed to be Tamerlan Tsarnaev - approached the man's car and "tapped on the passenger-side window.'' When the window was rolled down, the suspect opened the door and allegedly pointed a firearm at the driver.

"Did you hear about the Boston explosion?'' the suspect told the driver. "I did that.'' The suspect then allegedly removed the ammunition clip from his gun to display a bullet before reinserting it, saying: "I am serious.''

The gunman forced the owner to drive to a second location where the second suspect was picked up and took a seat in the back. The gunman allegedly then took the wheel, moving the owner to the front passenger side of the car. And while they were driving, the gunman demanded money, receiving $45. One of the suspects, according to the owner, also demanded the victim to surrender his ATM card and password.

When they stopped at a gas station and the two men left the vehicle, the "victim managed to escape.''

The incident immediately preceded the bloody confrontation with police where Tamerlan Tsarnaev was killed. His brother, who is accused of later abandoning the stolen car, was captured late Friday night, hiding in a boat parked in the driveway of a Watertown, Mass., residence.

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