I am definitely interested in the outcome of this so please do let us know. Keep in mind that if a self righteous person knowingly opened a package that didn't belong to them they are breaking the law! Try and not fret over this, it is possible it was mailed to the wrong address. Our UPS guy is always dropping packages off for us when we're not here when I know they are supposed to get a signature. I've often wondered how they handle that....
Good luck and don't worry yourself to death over this