In Russian, своеволие (svoevolie), "self-will" (our translation), joins своё, "one's own," and воля, "will, freedom." Kirillov says that the fullest point of his self-will is to kill himself, and that killing another would be the lowest point. Days earlier he had refused Pyotr any agreement: it was only his воля, and it remained only his.
Where It Appears
Quotes
I am obliged to shoot myself, because the fullest point of my self-will is to kill myself.