Some cases will be more complex to be solved. On some occasions, a “double” progress bar will appear over a detective’s head.

Those files are interdepartmental: they need to be checked by more than one detective on different investigation areas, so they will take more time to be closed. You will receive more money per hour when your people arrest those criminals!
 
Don’t forget that a warning symbol next to an orange progress bar will indicate some extra waiting time. Be patient!