UPDATE: The Washington Post works its sources and gets a little more on the motivation front:
The 19-year-old suspect in the Boston Marathon bombings has told interrogators that the American wars in Iraq and Afghanistan motivated him and his brother to carry out the attack, according to U.S. officials familiar with the interviews. ... Dzhokhar Tsarnaev has specifically cited the U.S. war in Iraq, which ended in December 2011 with the removal of the last American forces, and in Afghanistan, where President Obama has made plans to end combat operations by the end of 2014.
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Original Post 10:49 a.m.: Dzhokhar Tsarnaev was officially read his Miranda rights yesterday afternoon—more than two days after being taken into custody—but that doesn't appear to have prevented the 19-year-old from cooperating with federal investigators. CNN's Jake Tapper with the details:
A U.S. government source tells CNN that in preliminary interviews with the Boston Marathon terrorist attack bombing suspect, Dzhokhar Tsarnaev has told law enforcement that no foreign terrorist groups were involved in the incident; there was an online component to their radicalization—through watching videos, not through online communication; and that older brother, Tamerlan, was the driving force behind the planning and execution of the attacks.
Investigators, of course, will still have to independently confirm the younger Tsarnaev brother's story. (Even if he is telling the truth as he knows it, there's always a chance that Tamerlan wasn't completely honest with him in the lead-up to the attack.) Still, his account sounds like it lines up with the rest of the evidence. CBS News reports that so far the government has not found any evidence to suggest the brothers had ties to any major terror group, and two officials likewise tell the Associated Press that the pair were motivated by religion. That all appears to confirm what Tapper's source is telling him, namely that the preliminary interviews with Tsarnaev suggest that he and his brother fit into the classification of (in CNN's words) "self-starters, self-radicalized jihadists."
Dzhokhar Tsarnaev suffered a (perhaps self-inflicted) gunshot wound the the throat, and is largely unable to speak. He mostly only nodded during a short bedside hearing yesterday, although he is reportedly also communicating with investigators by writing out his answers.