I've recently read a little about cocaine. Here's how it pertains to the situation.
Cocaine causes blood vessels to clamp down and our heart rate to go up. The net effect is high blood pressure. As for which blood vessels - the most dangerous part about it is that it will constrict the coronary arteries which feed the heart. So now you have a heart that's beating fast and you've cut your supply line to it. That by itself could produce a heart attack. In fact from what I understand if you ever hear of a young person with a heart attack cocaine should be included in the suspicion somewhere.
And that's all before any activity happens. So add all the excitement on there and the heart is even more starved for oxygen. If a part of the right side of the heart dies from the heart attack there's high likelihood that you've messed with the conduction system - the circuitry that times the heart rhythm. I think ventricular fibrillation may be the most lethal arrhythmia to die from after a heart attack - not sure.
Could the man pinning her down have caused an arrhythmia by himself? This is an opinion but mine is leaning towards no. During CPR / chest compressions it is common to find that the ribs were broken - and they'd probably have to be in order to manually squeeze the heart enough to make it pump from the outside. It would take a pretty strong touch to mess with the conduction system from the outside. So it would help us figure it out to know if her ribs were broken. The other thing is that they did not say she died from being unable to breathe. So if the man pinning her down didn't do that hard enough to stop her rib cage from moving while she inhaled / exhaled , I feel it's less likely that he was able to push directly on her heart in order to mess with the conduction and cause an arrhythmia.
You only get one shot at life.
I didn't read the article so I don't know the family's stance. This is just hearsay but I was warned that a defender's action could be the most justified in the world but then relatives who hadn't been in contact with the deceased may come from all over - suing and swearing fierce loyalty. Or sometimes a family may sue just as an expression of grief because death isn't a good thing. Just something to take note of.