If you know it is a copyright infringement, you can probably be held partially liable regardless of the situation (I am not certain about this). Generally these waivers are for cases where you did not know. The theory I am using is that if you otherwise legally sold a firearm to someone knowing that he was going to commit murder, you would be considered a part of it. Its also worth adding that contracts that cover an illegal subject matter are invalid, so you may want to stay away from this guy altogether.
But to answer your question, a typical hold harmless clause could be found here:
http://itlaw.wikia.com/wiki/Hold_harmless. You might want to add something specific about copyright infringement.
Edit: You location says Columbo, is that in Sri Lanka? If so my advice probably amounts to nothing since it is US law.