I assume that's because he was going to kill him in the manner of some punishment based on The Inferno (level 8, ring for the flatterers, buried in excrement?), since they said he'd skipped the 7th, which I think they stated was suicide (which didn't make any sense to me-- each level has several rings, so it's not like "suicide" was the only option, besides the fact that in that ring of the 7th level, it's suicides who are being punished for their violence against themselves, not suicide as a punishment). I might be trying too hard to understand something that's just garbled beyond understanding, since all of this seemed very confused to me, and not just because I have no idea why this English teacher would decide to kill random mean dad figures in some simplified version of The Inferno, complete with totally unexplored student with bomb equipment.
I probably would have liked it a lot better if we hadn't seen the unsub so early and so much, and if it was either just killing mean dads, or just killing people based on The Inferno for some other reason.
The less said about Penelope dramatically swanning around Texas, the better.