Keep in mind it was a RIFLE. It may very well have passed through the intended target first. A rifle round can go through three bodies before finally coming to a stop. It can hit bone and change trajectory and continue on to go through a second body.
There needs to be more detail about the trajectory before this can be rightfully judged as an accident or neglect.
Good point! Although LEO should be using hollows to hopefully mitigate that. But this was too close to stop at first impact even for a HP.