I'm relatively certain the fatal rounds were not simunitions. I could explain but the simplest answer is none of the simuntions I've used penetrate like a pistol round and full load pistol ammunition isn't all that great when it comes to killing people. Simunitions ranges are normally very strictly run to insure live ammunition isn't present, and several brands require a ramped block in the pistol to assist in feeding the weaker recoil of the sim rounds. This block is also meant to prevent the chambering of live rounds. I can't imagine anyone working on a sim range without eye protection and gloves. Simunitions are weak but they will break skin and if you are hit at close range (under 10 feet) on bare skin, you will bleed, bruise and have swelling. It hurts a lot more than any paint ball.

My guess is that this incident was caused in the same way that many "dry fire" accidentals are caused. Complacency in checking for a loaded weapon. It only needs to happen once and your "dry fire" isn't so dry any more. Many departments have policy that prevents "dry firing" when not on a range or under the supervision of a firearms instructor because of these types of incidents.