If the guy had a heart attack because he panicked because someone had a knee on his neck, the cop still needs the book thrown at him. I get that determining what constitutes "the book" is determined by all of the circumstances. I understand why it took four days.
To me if the guy had 7 heart conditions and was high as a kite, the officer's actions still cause his death. The seemingly established fact that he kept kneeling on the guy's neck for almost three minutes after no pulse could be found is something beyond my comprehension.