Prosecutors said Tomasi used a knife and called it a "deadly and dangerous weapon." They also said he caused great bodily injury to the adult victim.
Tomasi and his girlfriend shared an apartment where the attack happened with their eight children. The defendant is the biological father of five of those children.
Court testimony revealed a rivalry between the defendant's 6-year-old son and the 7-year-old victim.
Prosecutors said the sibling rivalry was fueled by Tomasi who encouraged the boys to fight.
Testimonial reports revealed that on the day of the attack, Jan. 8, 2010, there was a series of family arguments.
Prosecutors said the mother stepped in to break up an argument and then Tomasi entered. He went to get a knife, returned, and stabbed the mother in the back. Prosecuters said he then stabbed the boy nine times.
/*Long Beach police/* officers found four bloodied knives, two of which were bent, hidden throughout the apartment.