In my game, for each case the game first decides on a random set of clues and then generates a completely new sim to match those clues and be the criminal suspect. So I haven't actually seen it able to use any of my existing sims as suspects, as it's highly improbable any of my sims are ever a 100% clue match for all six clues.
The game also has filters that prevent criminals and decoy suspects from being chosen if they're in the detective career. And it has filters on the employees at the police station being hired if they have the hidden criminal trait that only the correct suspect has.
So your situation could have been caused by mods you had previously active while the game was hiring police or generating criminals. Removing those mods after the game has assigned police and criminals wouldn't fix it.
How long was your play time between starting the case and issuing the APB? Do you play rotational style (i.e. do you switch between multiple different families and play them for a while) or do you only play a single family (which is your detective)?
