What does Islamic law say regarding the death of a young man who had been complaining of jinn, possession, and sorcery for six years, and who used to faint and have the jinn speak through him, then was found dead by strangulation, knowing that he was regular in his prayers and religiously committed?

One should refrain from delving into the cause of the brother's death and avoid definitively asserting that it was suicide or murder by jinn, or whether he was aware of what he did. One must supplicate for mercy upon him, give charity on his behalf, and think well of him, especially if he was diligent in prayer and knowledgeable of the rulings of his religion, for it is unlikely that he would intentionally commit suicide.