Police and prosecutors have incredible discretion when it comes to reporting violations and enforcing the law. Judge Alex Kozinski and Misha Tseytlin discuss that along with the issues of overcriminalization and the public's treatment of criminals in "You're (Probably) a Federal Criminal" (pages 43-56). A thought-provoking read about how and when a crime can be enforced and who can be considered a criminal.
The remainder of the essays in the book are interesting as well. They're all written in response to the first essay in the book. "The Aims of the Criminal Law", written by Professor Henry M. Hart back in 1958.