Based on the legal cases he has worked on, Thornbro said he “doesn’t remember a circumstance” when a first-degree murder charge got pleaded down to manslaughter. Initially facing a potential life sentence, two years later, Farinacci took a plea agreement for manslaughter and aggravated assault, court records show. Intent of crimeThornbro said one of the main differences between first-degree murder and manslaughter is “mental intent.” Thornbro told The Center Square that the first-degree murder standard is “higher” than manslaughter and “more difficult to prove.” Under Arizona law, a person commits first-degree murder if “intending or knowing the person’s conduct will cause death…with premeditation.”