Kung Fu Killer - Chinese movie (2014)

A vicious killer named Fung goes around Hong Kong killing top martial arts exponents and leaving a secret weapon called the Moonshadow as his calling card. When a convicted killer and kung fu expert named Ha – formerly working as a martial arts instructor before accidentally killing a man and being imprisoned and convicted for the crime he didn’t intend to do – hears of this, he offers to help the police catch the killer in return for his freedom.