Is the questioner considered a killer of his fetus and must he repent, given that he asked his wife to consume cinnamon and jump to prevent pregnancy in its early stages, then stopped doing so, and after 40 days it was found that there was no fetal heartbeat and it was aborted?

You must repent to Allah Almighty for attempting to corrupt the semen and abort it, because the preponderant opinion is that it is not permissible to seek to abort the sperm once it has entered the womb, unless its retention would cause certain harm to the mother. Indeed, Al-Dardir believes that it is not permissible to expel semen that has formed in the womb, even before forty days, and if the soul has been breathed into it, it is unanimously forbidden. There is no blood money (diyah) or expiation (kaffarah) due from you for what you did, because a fetus before formation does not incur blood money or expiation. As for the mother aborting this semen after it has ceased to pulse and its continued presence is purely harmful to her, it is permissible, rather obligatory, to preserve life if she fears perishing or severe harm from it.