NEW YORK -- Evidence obtained by investigators suggests the suspects in the Boston Marathon bombing case -- both Muslim -- were motivated to carry out the crimes at least in part by religion, said a source familiar with the investigation.
So far, the source said, authorities have found no evidence suggesting they had connections to Islamic terrorist groups. The two brothers, Dzhokhar and Tamerlan Tsarnaev, born in the Chechen region of Russia, practised Islam.
Dzhokhar Tsarnaev could face the death penalty in the April 15 bombings at the Boston Marathon that left three people dead and more than 170 injured, prosecutors announced Monday. Tamerlan Tsarnaev was killed in a shootout with police Friday.
Dzhokhar Tsarnaev, 19, is charged with conspiring to use a weapon of mass destruction "against persons and property in the U.S. resulting in death" and one count of malicious destruction of property by means of an explosive device resulting in death, according to the U.S. attorney's office in Massachusetts.
While Dzhokhar Tsarnaev and his older brother were on the run, one of them, while brandishing a gun, boasted to a carjacking victim of having committed the bombings, court documents show. A source identified Dzhokhar Tsarnaev as the one who made the boast.
"Did you hear about the Boston explosion? I did that," one of the suspects said, according to the affidavit supporting the charges.
A report detailing the carjacking of the Mercedes SUV, filed with the Cambridge Police Department, says the carjacking victim told police that two men told him "that they were the Boston Marathon bombers and would not kill him because he wasn't American."
He managed to escape, the report says. The name of the victim is not given.
A clerk in the Office of the Circuit Executive confirmed the filing Monday of charging documents against Dzhokhar Tsarnaev. He was charged at his bed in Boston's Beth Israel Deaconess Hospital in the presence of a magistrate judge.
Tsarnaev, described as alert and able to respond, was advised of his rights and the charges against him, and prosecutors stated the maximum penalties and moved for detention. Tsarnaev agreed to voluntary detention without prejudice, meaning he can still seek release at a future court hearing. He declined to answer bail questions, and agreed to a probable cause hearing on May 30.
The statutory charges authorize a penalty, upon conviction, of death or imprisonment for life, prosecutors said.
A White House official said the surviving suspect in the attack will not be tried as an enemy combatant in a military tribunal, according to The Associated Press.
White House spokesman Jay Carney said Tsarnaev will be prosecuted in the federal court system, and U.S. President Barack Obama's entire national security team supported the decision, the AP reported.
Tsarnaev was in serious but stable condition, according to the FBI. He had been unable to speak due to a neck and throat injury, the source said. He was also intubated and breathing with the help of a respirator and earlier, officials had said he was not in any condition to be questioned.
A source involved in the investigation said late Sunday the motorist carjacked by Tsarnaev and his older brother, Tamerlan Tsarnaev, 26, stated the young men planned to drive to New York. The source called such a trip "extremely unlikely" given the extent of the manhunt for the suspects after they fatally shot an MIT police officer, carjacked the motorist, and led police on a chase that ended in a shootout in Watertown, Mass. That assessment was proved correct by the events that followed Friday. However, that tip prompted authorities in Connecticut to be on the lookout for the brothers.
Authorities believe Dzhokhar Tsarnaev may have tried to shoot himself before he was taken into custody Friday night because of the trajectory and location of the bullet wound in his neck, a source familiar with the investigation said Sunday.
The shot was fired at close range, the source said, suggesting the wound was self-inflicted. He was found hidden in a boat in a backyard in Watertown, bloody and injured.
He was able to step out of the boat before being taken into custody after a brief exchange of gunfire with police and then negotiations with FBI agents, said Boston Police Commissioner Edward Davis.
Two men with connections to the brothers were taken into custody Saturday in New Bedford, Mass., and eventually arrested and detained on immigration violations by Immigration and Customs Enforcement, that agency announced.
The source said those arrests were made in an abundance of caution because the men were friends and former roommates of Dzhokhar Tsarnaev and had regular contact with him. Officials want to question them at greater length about whether they knew anything about the brothers' plans or provided any help to them.