Is one sinful if he does not visit his father’s killer who is mentally ill, and does the killer inherit from the killed?

If a person kills while insane, there is no sin upon him. However, it is not necessary to live with him, and it is not permissible to completely sever ties with him if he is among the kin whose ties must be maintained. There is no harm in refraining from visiting him if harm is feared. His aqilah (male agnatic relatives) must pay the diyah (blood money). The effect on his inheritance from the deceased or his wealth varies according to the different schools of fiqh. The Hanafis believe he is not deprived of inheritance, while the Malikis and Hanbalis believe he is deprived, even if he is a child or insane. Another opinion among the Malikis differentiates between inheritance from wealth and diyah. As for the Shafi'is, they deprive anyone who had a role in the killing. It is best to consult the Sharia court on these matters, and the person afflicted by magic should be treated with ruqyah.