Detective

Congratulations, you're basically a Security officer without Security access! You have a nice outfit, some cigarettes, thermals that everybody's gonna want to kill you for, a bottle of whiskey, and a revolver that's about as useful as sneezing on someone. If you want to be useless, go to the bar and become best friends with the bartender before blowing your brains out with his Russian revolver and have the chef cook you into something. If you want to be at least sort of useful, go yell at the Head of Personnel to give you the access you actually need to do your job and help take a bite out of crime with the rest of the redshirts, and maybe have Electronics scan your thermals if they feel like being useful. If you want to do your job competently and be the one detective in a blue moon who actually, y'know, investigates things, grab your fingerprint scanner and set your PDA to forensic scan (if you have it) and go looking for crime scenes.

Scanning blood will give you the blood type, and scanning items will give you a big string of gibberish that you can put into a computer in your office to check against the crew's fingerprint registry. Since tons of people use gloves anyway this isn't always going to be helpful, but scanning a discarded box of EMP grenades, finding one set of fingerprints, and tracing it to a guy who's been shady all round is a pretty good reason to hunt that guy's ass down and strip search him. Fingerprint evidence is not foolproof because, as mentioned, a lot of smart traitors use gloves, and the REALLY smart ones put spoof fingerprints on the items they use. However, considering how incredibly rare it is for the detective to do his job, most people aren't that paranoid, and will be utterly flabbergasted when you nail them with forensic evidence.

Note: just having a lethal weapon does not mean you should go around shooting people in the knees for trivial bullshit. Not only are your lethal rounds very very scarce and not that threatening unless you unload the whole thing into someone, the admins will be very mad at you for killing someone over a shove-and-fart. If you must use the useless thing, use stun rounds unless you're being chased by a changeling or a wizard or something. In almost every case the trusty flash/stun gun/stun baton set will carry you fine.