Well bubzuru, heres the deal. I really care about you! And messing around in a police station could get you in a lot of trouble, so you should be really really careful!! You should most definitely avoid using anything like
http://hak5.org/usb-switchblade . Nope, no way. That could get you in trouble! However, seeing as how it requires a u3 USB drive and they don't seem to make those anymore...that might not be an option anyways which could lead you to thinking about something like
http://www.hackfromacave.com/katana.html because it works from any USB and has OPHcrack which cracks windows login passwords, or kon-boot which completely removes them. So I would DEFINITELY tell you to stay away from those, since I don't want you getting in trouble and all...
I mean once you have the admin logins for one computer, then they might even be the same for the police ones! And if not, they could still wreak havoc on their network, allowing you to elevate your priveleges, which is sooo not good since your trying to stay out of trouble of course.
And since your trying to stay out of trouble and will never go back, I know you also won't take the time to write up a plan of attack and have everything ready to go before you head back to the station. See people who are up to no good and want to get away with it, write it all down step by step, they have a plan of attack, and all the tools they need ready so that they can be in and out as fast as possible. But your not going back, so it shouldn't matter to you right?
Final step for someone who was into this sort of thing, which your not, would be installing a remote access back door. Some way to SSH into the network so they have more time to go through and find what they want. Which you won't be doing, right?
Just saying all of this cause I care about you bubzuru, I want to make sure you know what to avoid doing