Until you confront the doctor with the evidence against him, the door can be lockpicked, and there is/was a key just south east of his house.
Try standing at the north west corner of the house; you may be able to see in and talk to the NPC in there, assuming someone wandered in while the door was open.
One person managed to toss a teleporter stone through the window on the west wall, but then the triggers to open the doors could not be used in the right order to get very far.
There are a couple other methods to get in;
FIX for the Missing Catacombs PortalTeleporting Anywhere, via hex editorWelcome to the forum. <img src="/ubbthreads/images/graemlins/wave.gif" alt="" />