If the thing was full of nails then we'll know it wasn't an individual suicide. But if it wasn't we still won't know. One wouldn't attach a "nail bomb" to a bus, I wouldn't think.
What I can't figure out is in the total absence of information about this event, at least that's being put out to the public, how is David Boren so utterly certain that this was a suicide versus an accident? I mean, if somebody blows themselves up, what about that event makes it certain that it was 'suicide' versus 'tragic accident?' Or possibly even an accident in the course of committing a criminal act, but that's another issue.