Interesting information taxiguy. Some of these numbers can be explained easily:

1992----90,804----(Redesign)
1993----99,860
1994----103,653
1995----96,458
1996----106,211
1997----110,111
1998----108,595----(Redesign)
1999----114,669
2000----92,047
2001----95,261
2002----79,716
2003----78,541
2004----70,816
2005----63,939
2006----62,976
2007----60,901

Rise in 1993 is probably contributed to the problems many officers/departments had with the 1991 Caprice. Just trying to change the rear tires on those 1991-1992 models was a pain in the butt.

The rise in 1997 is most likely due to the demise of the Caprice as the Crown Victoria was left alone as the only RWD police car available.

Decline in 2000 probably due to the introduction of the Impala 9C1.

Further decrease could be contributed to the rise in popularity of the Impala as well as other models (such as the short-lived police-package Intrepid and the Charger/Magnum).

Economic issues could also be seen as factors, of course.