When you get to the Dearborn police station, the yard where you need to go is surrounded by Deadites. You do not have to kill any of them. First, find the Spell Scroll that allows you to posses a Deadite for a limited amount of time,.This spell takes up three mana. Posses a Deadite, then run to the other side of the yard. You will find the Cypher and a envelope that you must take to the auto body shop. Note: The police Deadites will not recognize you as Ash, but the others will.