Okay, I managed to get into Matthias's apartment in Hibiscus Heights, and after getting shot a few times :^) I managed to avoid the cops by hiding behind the door (who would have thought THAT would work? Don't cops ever, y'know, look around?).
Now, unfortunately, I'm stuck in the stupid apartment. Clearly there's something I haven't done yet, but what? I've interacted with everything I can think of. What am I missing?