To commit murder (or manslaughter) the accused must be the proximate cause of the victim’s death.
If the officer’s knee hold did not proximately cause death, he is not guilty of manslaughter or murder.
So, no, you are completely wrong.
Maybe I’m wrong but I still believe when the cop kept his knee on an unresponsive man’s neck until he died, he is guilty of 2st degree murder which is not planned but when a situation arises and you use force to intentionally kill someone.