Exactly. If this was caused by anything intentional at all - that is, if it's not a gas leak or somesuch - it's a million times more likely to be the work of someone with a specific grudge against Yale, or at least against a specific person at Yale. A Unabomber-style mailbomber out to get a professor, and the bomb went off in the mailroom somehow?
Ah, exams were going on at the time, reports an editor of the Yale school paper (to Fox News! i'm amazed he'd deign to speak to Fox). Students are willing to go to extremes sometimes, especially if this is just a smoke bomb (there doesn't seem to be a lot of hard physical damage).
Historically, the psychological profile of a student who harbors a violent grudge against his or her school would, if to choose action, use a small weapon vs. a bomb that destroys an entire floor of the building.
In that case, it's a good thing it was law school. If it had been a science major it would have gone off in the wrong place. You'd think a lawyer wannabe would target the prof or the school by suing them.
there doesn't seem to be a lot of hard physical damage
I'd call blowing out part of the floor pretty much hard physical dammage.