As in most of the Series but more plainly clear in this one, when the F.B.I and police track down the stolen credit card used to buy the flowers. Derrick is outside speaking to the police when Garcia calls if you look his cell phone is switched off and he is in fact talking to a dead phone.
Only two shots are heard from the foster home, yet there are more than two photos with bullet holes.
Reid mentions serial killer Derrick Todd Lee using a recording of a baby crying to lure his victims. In reality, this is an urban legend.
Just before the Halberts are killed, Mrs. Halbert is on a land line phone when it goes dead (presumedly cut by the unsubs). The phone makes a "fast busy" signal when this happens. However, land line phones' sounds are all generated by the phone company, which also supplies their power. The phone should've been completely silent.
Cherry Hills village has notoriously bad cell reception precisely because of its lack of cell towers, so the neighbor's comment that there's a tower "around the corner" doesn't track.
When Morgan opens the door to a murder scene, he turns the deadbolt lock, not the doorknob.
When Carrie Ortiz gets up from the table after her argument with her parents, her father asks her in Spanish where she is going. She replies, "A lavar mis manos," intending to say "To wash my hands." However, no native Spanish-speaker would ever phrase the reply that way; in Spanish, the possessive is not used with body parts. She should have said, "A lavarme las manos."