G Police Cheats

Here exactly is how the Bonus Missions are unlocked without using the Cheat Code:
Mission 22 - If more civilians were killed than Nanosoft units, Secret Mission 1 will be selectable under the training menu.
Mission 30 - If the hit ratio displayed after mission was very good (over 70%), Secret Mission 5 will be selectable on the training menu. Complete the secret mission under the 1 minute 34 second time limit and Secret Mission 2 will become selectable.
Mission 35 - If the game is completed with all secondary objectives met, Secret Missions 4 and 6 will be selectable on the training menu. Otherwise only Secret Mission 3 will be selectable on that menu.