As someone who's done a lot of hiring and firing, the part that stands out most to me is not the sexual harassment part, but the fact that he was just hired and already is causing problems.

Normal people tend to be cautious and respectful at first. By immidiately jumping in and pushing boundaries, this person is demonstrating that he doesn't care about your company, he doesn't care what you or anybody there thinks about him, and he doesn't care if he breaks things and gets fired.

I would fire him as soon as I could without the lawyers getting up in arms. People like this tend to be very destructive. The smart ones will wreak havoc in your organization for years before you figure it out.