Scarecrow

A man who is obsessed with sex being sinful abducts prostitutes, tortures them for being attractive to him, and kills them.

Tropes in this episode

Action Survivor: Cherry, the UnSubs latest victims, manages to talk the UnSub into cutting her free, then stabs him in the back with a scissor and almost escapes before the FBI shows up to save her.
Bad to the Last Drop: Rossi tries the coffee in the police department. He throws it away after the first sip.
Lewis: "You are a brave man, Rossi."
Rossi: "Desperate times call for desperate measures."
Later:
Lewis: "What was that about desperate times?"
Rossi: "Turns out I'm not that desperate."
Cruel and Unusual Death: The UnSub inflicts this on himself, drowning himself in grain to atone for his sins.
Parental Issues: The UnSub's hang-ups about prostitutes stem from his father punishing him for fooling around with his girlfriend by dressing him up as a scarecrow and tying him to a pole in the middle of a field.
Scatterbrained Senior: Reid's mother is in a clinical trial for her dementia. It doesn't appear to make things better, as she calls Reid and is very confused.