I voted drugs/selling related, but I also agree with others that drugs are the basis but there is also revenge and a decision to get rid of those people. The killers left the three infants alive, they killed all the adults and the 16 year old but left a four day old newborn infant, another baby approx three months old and a two or three year old alive and unharmed. They were very specific about who was to be killed. There was nothing random about it.