U.S. investigators say that preliminary evidence from interviews with the surviving Boston Marathon bombing suspect suggest that he and his brother were motivated by Islamic religious extremism, but not linked to any terrorist groups.
U.S. news agencies reported Tuesday that government sources say that accused bomber Dzhokhar Tsarnaev has told them that he and his older brother Tamerlan acted alone. They were moved to set off the twin explosions at last week's race, the sources said, by a feeling that Islam is under attack and needed to be defended.
Tamerlan Tsarnaev died after a shootout with police late Thursday, while Dzhokhar was captured a day later. With a throat wound that was possibly self-inflicted, the younger Tsarnaev has been unable to speak with investigators, but has answered their questions in writing and with nods of his head.
Investigators cautioned that they are in the early stages of figuring out what led to the blasts near the finish line of last week's race that killed three people and wounded more than 250. CNN quoted one government source as saying that initially the Tsarnaev brothers fit the description of self-radicalized jihadists, with 19-year-old Dzhokhar saying that his 26-year-old brother was the driving force behind the attack.
The two brothers share a Chechen heritage, but both have lived in the United States for much of the last decade. U.S. authorities are investigating the older brother's six-month trip to Russia last year to try to determine whether he met with a suspected militant.
At Russia's request, the U.S. Federal Bureau of Investigation interviewed the older Tsarnaev brother several times about his possible radicalization, but found nothing suspicious.
The U.S. charged Dzhokhar Tsarnaev on Monday with using a weapon of mass destruction and malicious destruction of property, both of which carry the possibility of the death penalty or life imprisonment if he is convicted. The charges were read to him in his hospital room.
The judge who read the charges to Tsarnaev said she found him to be "alert, mentally competent and lucid."