I'm not sure how anyone can conclude he wasn't overcharged.I don't think he was overcharged.
The prosecution does not think they have enough to charge him again. Malice murder is essentially murder one and requires the prosecution to prove intent.
They're admitting now they cannot prove he intentionally murdered Cooper, so they clearly over-charged him.
So now, aside from the years he's spent in prison already, he's not guilty of anything at all regarding Cooper's death. Had they simply gone with felony murder, not malice murder, they wouldn't have needed to prove criminal intent. But now he gets off altogether. He's only staying in prison because of his sex crimes and he'll be out in a few years.
This is the prosecution's fault, not the appeals court's.