Even if the court proves that the police beat Yang, he still faces death penalty. Revenge killing is still murder and punishable by death in China's law. I know you want the court to prove the police is terrible, which I agree. However, that's not the best interest of Yang. His lawyer's priority is to save his life, not to make you feel good.

The only possibility for Yang to escape certain execution is insanity. He could very well be insane at the moment of killing even though he denies himself.