Im am on a vivec fighters guild mission where i have to kill this girl in the seyda neen census and excise office. I was able to sneak and unlock the door, but i cant kill the girl without my crime being reported! I need a way to kill the girl without my crime being reported, plz help!

try taunting her into attacking you. thus it's not a crime.

the proper way to do the quest is to talk to percius he tells you thats its not right. you can talk to her, but you really dont need to. just go back to the orc and tell him you wont do it. you wont get his final quest afterwards which is another pointless killing quest that will get you in trouble again.it doesnt affect your other fighters guild quest givers. in case your wondering his last quest tells you to kill a judge in ebonheart who just so happens to have guards everywhere.

don't worry about anything. just kill them. ie, taunt first and let them attack you. besides, you can gain money from selling what the dead bodies hold. ;)