The words written on the wall (erased by the homeless man) are different between the wall and the photo sent by Morgan.
The unsub, Rhett Walden, lives at 1503 Hope St, Washington, DC 20034.
1) there is no Hope St in Washington, DC
2) the address is missing the quadrant of the city. Since it was deduced that he lived in the Georgetown area, there should be a NW appended to it.
3) the Zip Code, 20034, is an unused code. Though the range of ZIP Codes for Washington, DC go from 20000-20599, 20034 is skipped (I.e., 20033 and 20035 are used). It's probably like the phone exchange 555; it's used in TV and movie productions to sound real, but it's not.
The scenes where Rhett Walden (Robert Knepper) interacts with the little girl in what is supposed to be Union Station in Washington, D.C., and where Hotchner, Prentiss, and Dr. Reid later find video footage of him, were actually shot in Union Station in downtown Los Angeles, recognizable among other things by its dark interior, high ceilings, and diamond patterns on the walls.
The BAU's investigation focuses on the Georgetown neighborhood. But the maps and street references they use are for the Noma neighborhood, just north of Union Station and 3 miles east of Georgetown.
Rossi states that the victim had trihalomethane in her hair, which Reid says is chloroform. Technically that is incorrect, trihalomethanes are a group of chemicals, one of which is chloroform, they are commonly used as solvents and refrigerants. The chemical name for chloroform is trichloromethane. It is an understandable mistake for Rossi to make, but Reid should know the difference and always points out small distinctions such as this.