How do you accidentallu stab someone...to death. And how many times did he accidentally stab her? The statistical probability would be enormously high and then skyrocket for multiples.
He didn’t do the stabbing. It was the knife’s fault. Bad knife just jumped into his hand and propelled the hand toward her. Time to ban knives, swords, sporks, forks, sticks, knitting needles, pencils and all other pointy objects.