emergency custody

In 2018 the courts wrongfully gave sole custody to my sons father. Since then I have had calls from CPS regarding my son being at parties where hard drugs were present. I called CPS a few months back to let them know my 4 year had been shown a gun and was actively around it. 2 weeks ago that gun was used by his father to shoot and kill a man. I would like to gain custody back of my son.