As a member of reddit, I can tell you this new story is misleading. Sunil Tripathi had been missing for a month before the Boston bombings. His disappearance was publicized, which lead to the speculation in some of the reddit community that perhaps Tripathi had gone MIA in order to coordinate the attacks. This was before the reveal of the Tsarnaev brothers' involvement. Tripathi's involvement was pure speculation, of course, as is a lot of information until investigations are complete. In all likelihood, Tripathi was dead long before the attacks.
I've seen some articles go so far as to claim that reddit's "witch hunt" lead to Tripathi's suicide, which is just as ridiculous as some members of reddit speculating his involvement in the bombings.