In my own opinion, it is not up to you to tag him with a negative trust, what I think you should do is what you have done, and that is reporting him the bounty manager, is it up to the bounty manager to tag him with a negative trust, and if necessary, ban him from participating in future bounties..
So what I will advice is that, you wait for response from the bounty manager, he is the one to handle the case in the best way, you can tag the user later, but wait for bounty manager to tag him first plus take other necessary action on him.
So you want me to remove my tag and let the bounty manager handle the situation first? It's just your opinion right? Coz' I have already tagged the user as it is not acceptable for me whether bounty or no bounty that he is taking advantage of my content that is not his and claiming it as his own entry without permission or consent.
The bounty manager doesn't have reputation either if he is willing to cooperate with me on this issue or not.