It's a bug or timer issue (can't remember which one). Download patches from ftp.sierra.com/sierra/policequest4/other/
I'm not sure, but you may have to restart playing the game since the saved game will be obsolete after patching.
Probably using slowdown utility like Turbo will also help (sorry I can't find the link), but you may want to try the patches first.
Have fun!
k: