The final quote given by Hotch is 'Nothing is so common as the wish to be remarkable.' He states that this is a quote by Shakespeare, but in fact, it is by Oliver Wendell Holmes.
The license plate shown on both the police car and the ambulance are standard Illinois civilian license plates. Municipally owned vehicles are actually issued special plates that are white with green lettering and have no background image.
When the son of the first victim starts to turn his father over, it's obvious that the father turns himself over. His hips move first, while his son is grabbing his arm, and the son never applies enough leverage to turn him over.
When the team is reenacting the shooting, the clock on the wall in the van isn't running.
While the team is discussing Landman in the office at the hospital at around 25 mins, a piece of thread can be seen on the camera lens during all but one of the office shots (at the bottom of the frame, towards the left).
In the beginning Hochner says the FBI doesn't refer to long distance shooters as snipers and JJ confirms that the FBI is perceived as not having a good track record with snipers. However at 42 minutes Hochner refers to the shooter as a sniper.
After shots are fired when re-enacting the shooting scene, you can see a car going backwards. On the road behind Elle.
When in the park, at times you catch glimpses of palm trees in the parking lot. Des Plaines, IL, is not in a climate for palm trees.