Key witness states on the stand he was charged

Key witness stated on stand ... the only witness physically at trial... that the victim tried to disarm him....charged at him... and the gun went off in the midst of a tussle. How does heat of the moment justify premeditated first degree murder. Let's get justice for him. All we request is they lift the premeditated first degree and drop it to manslaughter and free him so he can go on with life. He has given them 15 years of his life.