IMO, notable fact is that this was an arbitrary execution :

He was disarmed (carried a concealed gun but it was taken away from him in the moments leading to his death)

He was not resisting (although there was a bit of scuffling, he quickly ended up cowering on the ground, both hands on the ground).

The ICE agents could not have really feel threatened in any way (a single woman in company of Alex, pepper sprayed and being restrained, a sparse number of onlookers filming some distance away, probably less then the total number of agents).

Something like a full charger was unloaded into the victim.