Honestly, laughing at them is a good reaction, since it throws them off guard. Unfortunately, it can also lead them to being more vicious as they get angry. You're lucky it simply made him clumsy this time.

I don't suppose you can share a link to the new post? Maybe Reddit can find the next person before they become a victim?

Also, though I'm sure the police have done this already, it would be interesting to go back to the first known victim. There's this thing in criminal investigation called murder mapping, used to work out where serial killers are most likely to live. The theory is that their first murder is committed closest to where they live, and as they grow more confident - continuing to kill without being caught - they choose places further away to kill their victims. You've found several cases already, so you have the locations. After all, this person is only human, not supernatural; they can't cover huge distances in a second.