Instructions
Go to the entrance of the cemetery after you have completed the "Anatomy of a Crime" quest toward the end of "Chapter 2." Talk to the gravedigger and you will have a lengthy conversation. At the end of the conversation, select the option that allows you to ask for the key to the cemetery.
Listen to the gravedigger's demands for getting the key. He will tell you that he will give it to you if you get permission from Vincent Meis to access the cemetery, or clear his debt with Thaler. Both Thaler and Vincent are located in the same area as the cemetery. Choose one to talk to and head North of the cemetery.
Find either Vincent or Thaler. They both can be located on the same street which runs East and West two blocks North of the cemetery walls. Whichever you choose to talk to will begin a quest in which you will prove them innocent of committing the crime and either get permission to enter the cemetery or clear the gravedigger's debt.
Return to the entrance to the cemetery once you have cleared either quest. You do not have to complete both quests in order to get the access key to the cemetery. Tell the gravedigger you have completed his task and he will give you the key. You will also gain 1,000 experience points.