From that point, Tsarnaev was raced to Beth Israel Deaconess Medical Center, where investigators hope to get answers to questions about motive and the possibility of accomplices.
TIMELINE: From Terror to Manhunt to Capture
Nowhere were there more questions than at the University of Massachusetts Dartmouth, where Tsarniev was known as just an ordinary student.
"Literally, when I seen him he was just regular. He walked past me, we had a brief conversation and then I asked him for a ride home and he told me, 'Yeah,'" said Andrew Glasby, who lived at the same dormitory where Tsarnaev was staying after the marathon bombings.
Another friend, Zach Bettencourt, even asked Tsarnaev about the bombings.
"I talked to him in the gym about the bombing and he was like, 'Yeah man, tragedies happen all the time,'" Bettencourt said.
The night after the bombing, Tsarnaev tweeted, "I'm a stress free kind of guy."