Wiktionary
self-slain
a. slain or killed by one's self.
Usage examples of "self-slain".
And the body was that of Noureddin, self-slain, who in this manner had not only fulfilled the injunction of the Cadi but had also kept his bargain with the ghoul by providing the required number of corpses.
And that look in the staring-eyed faces of my grandmother and self-slain uncle might be sheer fancy on my part - sheer fancy, bolstered up by the Innsmouth shadow which had so darkly coloured my imagination.