In July 2011, on the hottest day of the year, I received a fragile-looking Maxell compact cassette from a retired psychology professor and gerbil-aggression researcher named Gary Davis. I had been told the cassette contained a recording of two police officers discussing their involvement in the robbery and murder of one Steven Pollock, a physician and pioneering mycologist who — despite invaluable contributions to the field, including an improved technique for growing psychedelic mushrooms on Purina Dog Chow — remains largely unknown. Carefully labeled police crook 6/17/81, the cassette had for thirty years been stored in a toolbox under…