Why are you assuming random? Maybe it was someone they helped out and had a distant connection (seemed like very trusting nice people), someone they hired, a handyman, a delivery guy, another local doing odd jobs, helping out. All of these people could have a troubled past given the neighborhood. They would also potentially have access and familiarity. Maybe didn't want it to go down like this but needed a fix, strung out or high and not thinking straight. Lots of possibilities obviously. A simple double tap to the M and a single tap to the FM seems like a surprised reactionary shot response to me.