The Character I'd Pick Out of a Line-up
"He watches the locomotive pass, and he turns to face the mountain. The train will slither into the tunnel, the new tunnel that replaced the one John Henry dug a few yards over. John Henry's tunnel didn't stand the test of time, the roof gave in, and they built the new tunnel adjacent, according to modern specifications. Obsolete.
He can't help it; he looks up at the mountain and finally gets confirmation of his fate" (Whitehead286).
Though I'm not much of a gambler, if I had to bet on who the shooter was at this point, my money'd be on Alphonse. (Don't get excited. I have no money, so this is hypothetical in more than one way) Obviously there's the chance that Whitehead is purposely trying to mislead us, but I think it's safe to say that we're at least supposed to have our suspicions about Alphonse as the shooter. One example of Whitehead's leading is that Alphonse decided not to take part in a shooting game, because he thought it would be "perverse" in light of his planned actions the next afternoon.
The text quoted above provides partial motive for whatever action Alphonse is planning on taking "tomorrow afternoon." Alphonse feels obsolete; as though he's no longer useful/needed. His wife doesn't speak to him and he has no children. The not-having-children thing seems to be a sore spot for Alphonse, who thinks "he has smaller hands, but he could take a smaller hand in his own and lead," and also, "He has things he could pass on to someone, a message to communicate beyond tomorrow's dispatch" (282).
Obviously I'm not saying these are good reasons to go on a shooting spree, or that there are good reasons to do such a thing, but these are the motives we're shown. I wouldn't be surprised if the shooter turns out to be someone completely unexpected, but Alphonse is not sending out the sunshine-iest vibes.