We need to have more detail, such as what kind of harassment is taking place; sexual, threats of violence? If violence, then consideration should be made about filing a complaint with authorities? Are other people being harassed? How do you know HR concluded its investigation? Regardless, your boss sounds like he is clearly going to continue and you need to do something about it.. If you have a handbook, review it's procedures including the right to appeal if it should turn out that the complaint was denied. It is not at all unusual for companies to drop the ball with regard to these type of investigations. Often times, they just want everything to go away. But if this is a pattern, then you have to come up with a strategy to have this boss' behavior addressed. I highly recommend you meet with an attorney who specializes in this area. If it is going to escalate and get worse, you want to be able to know your rights. Go luck.