Click on the hint you need based on the last item that you opened.
Hints may be broken down into multiple steps to help you open the next lock. There is also an 'evidence hint' button if you need help deciphering the evidence to narrow down your suspect list. Click the 'home' button to return to this screen.
Each hint is password protected so that you cannot skip ahead. The password for each hint is the same as the code you used to open that box. If the last thing you opened used a key, then the hint password will be the code from the previous lock you opened.