Thanks to MikeM for providing two vintage photos of a true FBI Mustang. It is a SSP that has the same DSO number as other confirmed Government cars. This one is interesting because it was used at Quantico for EVOC training purposes.
http://www.specialservicemustang.net...info161602.htm
Note, this is not the car used in the movie "
Silence of the Lambs", which was a civilian coupe. As I understand it, that car and this SSP were both crushed.