Refugee center

Hey guys!
I am quite new to this game, and I just found a refugee center with nobody inside.
The upper right chunk of the center is not accessible. I tried to smash open a locker in the way, but then there is an iron door hiding behind the locker.
As I then heard metal screeching from that room, I stopped trying and assumed that there are some zombies inside.
But why? Why there are zombies in the refugee center? Why there are not even a NPC there? This is quite weird and not as I expected. The refugee center I thought about should contain at least 5-6 NPCs, but there are none.

Mine was like that once, but then I realised that I’d left Static NPC’s off. Make sure first that you haven’t done that. As for the Zombies, the NPC’s will tell you a small story about that when you find them.