Fire that person immediately, it's a clear breach. You need to show your employees that you will support them when something like this happens.
This may not be the first time this has happened, might only be the first time that you have heard about it. You need to be proactive in creating a safe work environment and as the founder that is your responsibility.
The United States of America have a sexual harassment policy. They also have theft and murder policies. This isn't a matter of company policy, although covering up these things may be.
By having them agree to the policy, it makes it easier to settle the dispute.
If you are talking about the EEOC, then you are only talking about sexual harassment in a workplace with 15 or more employees. Also, it is a concern for the company, not the harasser; while it is antisocial behavior, it isn't a crime.
Does this matter? Most employers don't have a murder policy. In both cases, laws supersede policy.