Went to get some tools out of a dark corner of the garage and found this...
Measured out about 5'3"" so he's a pretty good sized feller. I'm no herpetologist but I'm guessing a rat snake; I've had a few of them around the place. I'd just as soon he's moved on; I hate to be a wimp, and I know they do some beneficial things, but I'm not really a snake guy, and if he's still in there I know he's just waiting to scare the bejezus out of me some time. If he is I doubt I have any mice though!