It is America’s first fully interactive national tragedy of the social media age.

The Boston Marathon bombings quickly turned into an Internet mystery that sent a horde of amateur sleuths surging onto the Web in a search for clues to the suspects’ identity. And once the search focused on Tamerlan and Dzhokhar Tsarnaev, the brothers’ social media postings provided a rich vein of material to mine and sift.

There are more than a thousand messages on Dzhokhar’s Twitter account in addition to a profile page on VKontakte, a popular Russian social networking site, and in Tamerlan’s case, a list of favorite videos on YouTube and what appears to be an Amazon wish list belonging to him (Amazon would not confirm whose list it was, citing its privacy policy.)

These posts instantly became dots that people began trying to connect. Some details ratified the views of those former friends and neighbors who said they were utterly shocked at the brothers’ possible involvement in such a horrifying crime. Other posts pointed to Tamerlan Tsarnaev’s growing interest in Islamic radicalism and possibly a dark subtext to the friendly, boy-next-door affect of Dzhokhar.

At the same time, they were reminders of the complexities of online identity — of the ways in which people strike poses and don masks on the Web (which can sometimes turn into self-fulfilling prophecies), and the ways in which the Web can magnify or accelerate users’ interests and preoccupations.