No one will state that on record, but the doctors are reporting ball bearings and lower body injuries. The Doctor from North Carolina that was treating people on the street described all lower body injuries including a man who had both legs blown off. Not removed in a hospital, but on the street. The hospitals report over 10 amputations, but do not say how many people that represents.
They are saying the online sites that teach how to build these devices recommend ball bearings.
I'm still betting on a domestic male under 25.