On Criminal Minds Season 10 Episode 4, the BAU investigates the cause of death when a man wanders out onto a busy highway and is killed.

A few days prior, the man had received a phone call from a throwaway phone. When that same phone calls another number belonging to a research scientist who later turns up dead, the BAU realizes they have a serial murderer to find.

It turns out that the murderers revolve around the killer's belief that he is infested with cockroaches - only no one will believe him, much less help him to get better.

How did he get that way? And why did he have such a pressing need to convince others - upon pain of death - that he not only had a problem with infestation but needed help to get rid of it?

You can find out when you watch Criminal Minds online.