Towards the end when the unsub is in search of his next victim, one of the extras seen walking down the street is in fact the girl who was killed at the beginning.
When the B.A.U. are in the conference room talking about the profile of the killer, Reid's watch goes from being over top of his sweater sleeve to under it.
As the team is talking in the conference room (at around the 17-minute mark), JJ shows a map of the three major hubs of prostitution activity. The next shot shows the window on the left side with the reflection of a crew member in a white t-shirt and the camera operator.
At 5:40, Morgan and Prentiss are interviewing two "working girls" under an awning (where the victim was lying in the prologue). At the bottom right of the screen, three fingers can be seen, of someone holding the bars of the awning in place.
Dr. Reid is shown walking up the DC Metro stairs, but just seconds before footage of a train arriving at the 59th St subway station in NYC is shown.
Reid is shown taking a subway to work. But Quantico is 40 miles away from any commuter rail network.
Around the end when they are on the streets searching for the unsub, a bus drives by. The bus is from Montebello Bus Lines in California.
When the team is coming up with their initial profile, there is a white board behind Gideon. It is a notice for a mandatory seminar. Mandatory is spelled incorrectly. It is spelled "manditory."