Even with my limited experience, I once saw how, even in very suspicious circumstances, if a person lawyered up very early into the investigation, and refused everything, polygraph, etc. and spoke only in the presence of a lawyer, it became impossible to prove involvement. Probable cause is hard to prove, in the US the law is THE LAW. I imagine the Delphi situation, when so many people needed to be spoken to in the beginning. I would assume many could have lawyered up, and how difficult and time-consuming it must have been. The investigation could have been stalled by some refusing to cooperate, or being marginally cooperative. It doesn’t imply that they were involved; simply, the murders were gruesome, and with this, innocent people were scared to incriminate themselves. DNA sweep is purely voluntary. And putting myself in the shoes of the Delphi parents whose kids were outside on that day, or simply used to frequent MHB, I imagine thinking, “what if it was my kid?”, or even, “what if they think it is him?”... Just imagine how in must have felt. All articles advice us to lawyer up in such cases. And we all say, “a tiny place of 3000”, but maybe, it is not so tiny, when LEOs have to talk to so many people? I understand, there was an army of police and FBI involvement on one side, but probably, an army of lawyers, on the other one. JMO. Tell me if I were wrong.
Nobody here can quantify or characterize how many people cooperated or didn't cooperate with the Delphi investigation. That's a question for the investigators to answer. We can assume some cooperated fully and some refused and everyone's reasons for their choices were multifactorial.