His mom is dead. Usually kids like this have either witnessed an abuse, taken part in an abuse or have been abused. Whichever it is, he should be held responsible, even if he is only 10 years old.
He needs to be set apart from society, hopefully with some sort of therapy. Then he needs to be tried for murder when he is an adult. The worst thing that could happen is for this kid to be allowed back into society without paying for his crime.