John E. Douglas is a former FBI agent and one of the first profilers. He was instrumental in the capture of numerous serial killers, and has gained international fame as the author of a series of books detailing his life tracking serial killers. They are considered to be some of the most insightful works written on the minds, motives, and operation of serial killers, and the methods and lives of those who track them.
Douglas also works as a consultant, most notably in the JonBenet Ramsey murder. The Jack Crawford character in ‘The Silence of the Lambs’ was directly based on Douglas.
Source- Wikipedia http://en.wikipedia.org/wiki/John_E._Douglas