I'm a trained Force-On-Force instructor, using Simunitions. The protocols are very strict, and all training is conducted within a "sterile" area, into which no live ammo or weapons are allowed.
This tragedy clearly occurred outside the training environment, without instructors. Force-On-Force training using Simunitions is safe. The officers involved in this incident were acting against their training, or, if untrained, beyond the scope of it.