So by the son's account, the father was just fine handcuffed in the back of a cruiser. Just by stating what we know for sure to be true, somewhere between arrest and release, he was beaten so badly that it fractured ribs and vertebrae. His injuries were not treated or investigated until after he was released. A crime in and of itself in California. No charges of battery on a police officer, resisting arrest, or even dissorderly conduct. Now starts the conjecture. Had a legit scuffle happened, why would the officers not submit charges for the previous crimes just to cover their ass? To have a record of what happened so that this guy couldn't just make up a story?
At the very least they beat the hell out of a guy while he was in custody, no matter how much he was resisting. Circumstantial evidence of a department completely out of control and some suspicious behavior by the police would point to this guy's story being at least somewhat true.