Since it is not typical for American homes to be rat-infested, one might reasonably wonder what caused the infestation that resulted in this tragedy.
Though that was probably not the case here, they can get into new homes where the ground has recently been graded from "woods" to home sites. I had one here and there sneak into a new home a number of years ago through an open garage door. They're pretty quick. After that, they only need get through the sheet rock.
The city caused it?
Last winter we had a family of rats move into our basement.....Keep in mind that our finished basement is about 2000sq ft with numerous ducts, drop ceiling, conduit runs and hollow walls.
We had a terrible time getting rid of them. We first tried humane traps but quickly moved to poison and snap traps....They are incredibly bright animals for their size and it took us two weeks to get them all. We actually had them invade the main house from their basement "base" and leave their little droppings in the Kitchen and a chewed door edge in a failed attempt to get into the pantry.
You have to assume that they had full run of the house at that point while we were asleep. We had the kids close their doors at night to their rooms. Very Creepy....
Our home is in a very upscale area of North Atlanta, not the projects.