Start the game with:  

CARMEN cheat  

Then, when you select 'Options' one of the choices will 
be a cheat menu.

Or, if you prefer to edit saved game files:

Use a hex editor such as DISKEDIT to find your name in the DETECTIV.DAT
file.

Make believe that the first letter of YOUR name is BYTE #1.

Byte 23: Your Rank
0 = Gumshoe
1 = Investigator
2 = Sr. Investigator
3 = Inpector
4 = Sr. Inspector
5 = Detective
6 = Master Detective
7 = Super Sleuth

Byte 24: Number of completed cases