I don't think Satoru got a chance to look at the "previous suspects" list. Airi called her phone just as he was about to look at it. He only knows the "remaining suspects," which he strongly believes aren't the true killers.

Now that we've gotten a slightly better look at the killer, I find it hard to believe that he is all that much older than Satoru. They might even be close to the same age. That means that Satoru could be looking for a peer or at most a high school student. This gives credence to the "multiple suspects" hypothesis, because I doubt the modern day killer was murdering up to 6 middle school girls (and one boy) all on his own. More like joining in the act and now taking up the mantle.

Though, given that I also assumed Hiromi was a girl who hung out with the boys in the class, and the leading theory is that he was murdered to throw off suspicion from people close to the victims...the likelihood that a classmate (or relative of a classmate) is involved is astronomically high. They'd be pretty much be the only ones who would know.