Animal control lied to you.

You cannot simply have a animal in your possession for three days and it automatically becomes yours. If that was truly law, then a lot of very pricy animals would be stolen on a daily basis and hidden for that 3 days.

I'm not saying that you "stole" the kitten. Obviously, you picked up a abandoned kitten. But TECHNICALLY by law(at least in my state), you must attempt to find the owners for ten days, THEN the animal is considered abandoned. But you must make a attempt. The most common "attempt" is to put a vaguely worded ad in the Lost/Found section of a newspaper(usually free) and after that, you're usually golden.

But IF it were a owned animal and the owner finds out you have it and you cannot prove you made a "reasonable" attempt to the judge, then it's the original owner that will recieve the animal back. In your case, the woman would easily have been charged with neglect IF she could possibly prove it was her kitten, which she could not. She would probably also be charged with "endangerment" for placing kittens outside in a box like that. Since the box was placed outside without supervision, that could possibly be stretched to be considered abandoning the kittens(same as if she put the box out beside the highway and drove off, sort of).