Corrected entry: They are confronting a man who may be the unsub when Emily Prentiss says that the victims all have blonde hair and blue skin. Obviously, the victims have blue eyes, not blue skin. (00:18:17)
Corrected entry: In the scene where Jordan is describing the case, the writers made a large error concerning the M.O. of the UnSub. Agent Jordan states that the UnSub makes his victims clean up their own murders, and they arranged the cleaning supplies in a triangular pattern. The cleaning supplies were bleach, ammonia and garbage bags. This would be excusable if she hadn't also added that both bleach and ammonia were found under the victim's fingernails. If you mix ammonia and bleach, it has the potential to create one of three very dangerous chemicals. One was used in WW1 (chlorine gas), and the other two are highly explosive (Nitrogen trichloride and hydrazine). However, all the victims died of exsanguination (blood loss). This isn't mentioned by Dr. Reid, who has a Ph.D in Chemistry.
Correction: It's not necessarily a mistake that Dr. Reid didn't mention the potentially dangerous chemical combinations; since the victims died of blood loss and not an effect of toxins, there was no reason to bring it up even though it would have fit his idiom as demonstrated in other episodes.
Corrected entry: The Reaper (acting as a police officer) asks for the driver's licence, registration and proof of insurance. This episode takes place in Massachusetts where proof of insurance is on the registration. Police only ask for licence and registration.
Correction: As you said in the entry, the Reaper was just ACTING as a police officer. Its entirely possible this wasn't known, as he may not have ever been pulled over.
Correction: Prentiss was referring to the fact that the man liked dead women, when you die skin turns blue.