My Ex Physically Abuses My Son

Location: Arizona. My ex, father of my child grew up being abused by his mother. Our son has a history of lying, and getting in mild trouble at school (he popped syrup on a few kids on picture day, minor but definitely unnecessary actions on his part). He is currently in trouble for damaging someone's car, he did not do it intentionally but was being careless. His father took him for fall break, and proudly told me today that he beat his ass with a belt for his behavior and will do so every time our son lies/misbehaves. He is doing it with the intent to physically harm him, to "teach him a lesson, it was done to him as a child." I am picking my son up tomorrow and first checking if there is any bruising or physical evidence, but I would like to record my son without him knowing to get a genuine response from him and ask him if he feels safe/unsafe when he is with his father. My son is 11 years old, and it makes me sick to think of him getting beaten for making mistakes, let alone being beaten with a belt. I want to report his dad for child abuse, I am waiting until I see my son tomorrow to see if there are physical marks on his body. If there are, and if he does feel unsafe with his father, do I have a case against him? My son has told me that his dad and his girlfriend often have such aggressive arguments (my son is his eldest child, he has a step daughter and they share a son together) that he has to take his younger siblings outside to stay away from their yelling. And if they try to come back inside while they are still fighting, they get screamed at to go back outside. They do not live in a good neighborhood either, it does make me nervous that kids are out on their own so they don't hear my son's father and his girlfriends arguments. I want to call CPS and report him, but I'm getting mixed reviews from family about it. Do I have a case?