Other mistake: While Hotchner and Reid are talking about Hollow Man and the Mill Creek Killer, Reid's going through the newspapers and when he figures out that the two killers have been talking to each other via the classifieds, there are two closeups of an ad's text. After Hotchner suggests using their relationship against them, Hotch says that Reid's fake ad will imitate Hollow Man's language patterns to send a message to the Mill Creek Killer. Then we hear Reid reading the fake ad they just placed in the classifieds, but the problem is it's the same ad that was shown in the closeups earlier, plus an additional line at the end - "here's my gift to you."
Empty Planet - S2-E8
Other mistake: In Empty Planet where the exploded bus is shown, there is an evidence marker with blood spatters on it. The blood wouldn't be there if the marker was placed after the event had occurred.
Other mistake: In the opening scene, the UnSub is wearing breathing apparatus, however his smoke hood is under his face mask. Wearing the hood under the mask would make it impossible to get a face seal, and as such would let smoke into the mask.
Chosen answer: Back in Target Rich, a hitman named Giuseppe Montolo dies whilst being interrogated by Derek. The men who abducted Derek were hired by his father, Chazz, who seems to blame Derek for his son's death. It's explained further in A Beautiful Disaster.
Annabel Keeley