This article details how confidential informants might run into trouble. This was going on in 1974 using underage kids who were in minor trouble. Is it possible something like this was a factor in this mystery somehow? It might explain the hush-hush nature of some aspects of the case. https://www.google.com/amp/s/www.newyorker.com/magazine/2012/09/03/the-throwaways/amp