I never read that that angle was covered.  But I don't know if the two people that wrote books considered it.....but they should have.  The authorities should have considered it.  I followed this case (in the media) from start to finish and beyond.  It seems too much of a coincidence that he changed his insurance policy to his parents then wrote a letter to them....."that if he were killed".  It made no sense that he thought he would be killed.  Huges/Linehan also had a 1 million insurance policy.  Why didn't Lippink think someone might kill her?  After all she was supposedly stringing 3 men along.  Also Carlin's son had an attraction to Huges/Linehan.  Lippink may have talked the boy into shooting him.  Convincing him if  he Lippink were out of the picture and Hilke had already left.....why then Mechelle would be all his and his dad's!