Oh, geez, that totally sucks!! I have had wild mice break into some of my tanks in the past and impregnate a couple of does. It figures though, that a wild mouse would do that. I took measures so that won't happen unless I just plain make a mistake about how I leave the tank. Wild mice are a real bother, and we live in an old house, so it's impossible to prevent them from getting in. I've had wild mice show up in empty tanks that hadn't been dumped and cleaned; I think they like the water bottle not to mention left-over food.
I'm horrified to hear that one of your bucks was killed by the wild one, and bummed that you lost yet another litter. It's time for you to get that wild little fart dead or alive!