Because it is required to show, because it is a prevalent disease in the area that is reportable and they will exterminate your flock if they have it.Now you have to answer questions
Why did you vaccinate?
It's free, and it keeps them safe from developing the very common (and deadly) disease.

Sounds like a raccoon or a fox. When we lived in Aus we had a coop with a pen outside that was around 7 feet tall at least. Foxes could climb over it, they are sneaky little buggers. I would imagine it was a raccoon in your case however. I am also guessing that it is going to come back now that it knows where it can pick up a free meal, so I would try and cover that hole with a metal mesh or something

