In the novel Klaus still didn want to believe Wendelins fathers story about how his son died and we e left wondering which is the truth. However, if you think about it, at this point Wendelins father no longer has any reason to lie at this moment as he has lost everything except his family and will be exiled. Also, based on his version of the story and what just happened with Wendelins brother, it shows us that excessive greed can definitely make a person do horrible things even to their own family and friends. Klaus son had the position to inherit a large portion of political power in their region and also the ability to marry not only a prized woman but also inherit her familys support. Hein might have been driven to a lapse of judgement by greed and envy when that instant a chance presented itself to him where he can possibly get away with murder and take all he wants for himself. It doesn help that he might have indeed carried some resentment as told when the two were seen arguing in the past. Klaus can accept that his son and his friend would fall into such a tragedy and so he constantly denies it.