I think if we go back to the issue of the detectives saying that there was an hierarchy then what he says does not destroy any theory of thinking that the ones at the top of the food chain, order these killings, probably are, very intelligent and very organized. They are not the ones doing the physical kidnapping and may not be the ones placing the Vic's in the water. Think of the Mafia, the people at the top come up with the plans and strategies. They hire punks and thugs to take care of the work they don't want to dirty their hands with. Yet they call the shots.
I think we are looking at a similar structure here, just not the Mafia. The top of this particular group is intelligent and organized..thrilled they have found a way to do this for so long without being caught. The people that are part of their group are the followers , who will do what they are told, exactly as they are told or risk their own demise. There are probably both personal and private gains for them. These people who are acting for the top would be the ones who would not have done well in school, nor been popular. They are more then willing to help with the demise of these targets that the intelligent top has picked.
I think the detectives are putting the message out there to let these people know they are getting closer and they know how the group functions. And also beware to the worker bees in the group..they are saying they have their number. Maybe they are hoping some of them will give up info to save their own selves.