Just did some testing on a copied hood. Everytime an apartment sim would walkby that I haven't modified, I killed it. I ended up with 21 kills, which got rid of most of them. (The walkbys became a maze of tombstones
) Then I jotted down the walkers.
Out of 50 walkbys:
15 were original sims.
7 were then killed. (apart. sims)
the other 28 where walkers which consisted of just 5 sims.
I'm assuming the game isn't using pure random function to decide who goes. It appears to favor the newer sims a lot more.