Testimony showed that the knives Monelli used were found behind a kitchen stove and one of them had his palm print, the newspaper reported.
According to NJ.com, the child testified he watched from his bedroom as his father choked and stabbed his mother before telling the sobbing boy, "You shouldn't have seen that."
According to trial testimony, Monell moved out of the home in April 2016 after a domestic violence incident, the Daily Journal reported. He was arrested two weeks after the crime in Atlantic County, NJ.com reported.
Monell rejected a plea deal in October, where he would have served 30 years to life imprisonment, the website reported. He now faces a mandatory life sentence without parole.