To my credit, I did not know he was a boy (about 20 or so) or mentally challenged at the start. As I was walking to go find him, we decided that Sandy and I should go to the police station and let them deal with it.
We got to the station and the police knew the boy. We walked around the town with the police looking for him. They decided to go to his home, and a few minutes later they brought the boy in and things got very strange. At first he was screaming something that we guessed was, "no way I would grab a middle aged woman's butt". Either way, at some point he owned up to it, the police scared him, and he apologized over and over again. What a creepy hour.