[sgxin]

oxygen is precious
they died from hypoxia not becos there is a lack
the mitochondria stop

Most of them should have dead from suffocation due to the huge crowd.
The pushing force within the crowd are cumulative and the force exerted on those at the middle, or those against a barrier/wall, would probably be 100kg or more.The rib cage muscle simply couldn't work under such a heavy crushing and thus breathing stops.

Another dangerous effect of cumulative force will be tug of men war.
When 10 to 20 individuals on one side start pulling, the tension in the center of the tug rope can reach more than a tonne.
There was once an unknowing participant who wrapped the rope around his arm and it just snapped when the pulling started.