As you and your friends walk along a lake shore you come across a young man basically repeatedly dunking the head of older guy in the  water?

and you tell him to stop it and he does not stop. He continues to repeat the process each time dunking the head of the older guy who looks like he is at least 70 years old under the water and keeps it there for a good 8 to 10 seconds bringing it up for maybe about  8 seconds and dunking it again saying this is what you get for messing with me.  Anyway your group calls the police who arrive on the scene and fortunately they arrive within 3 or 4 minutes. Unfortunately by the time they do, the old guy is already no longer breathing and is pronounced dead on the scene. 

At the trial, the defense says the official cause of death was a heart attack not drowning, so his client cannot be convicted of drowning the guy as he did not drown. Furthermore it is proven that the older guy had a series of health conditions including emphysema, high blood pressure and a previous mild heart attack.  The defense claims that the guy was already very sickly and that this is why he died.

Will the verdict be innocent as the defense has a death certificate saying heart attack and not drowning.