Forensic Sciences

If you find that someone has written a Ph.D. dissertation on your topic, you can be absolutely sure that the author did exhaustive research on the topic. The dissertation will include a lengthy bibliography to document that research effort. Use this existing list of resources as a starting point for your own research. Dissertations and Theses Global is a good place to search for dissertations on your topic. 

Look for bibliographies at the end of scholarly journal articles, essays and books. If you find material that is right on-topic, odds are that the author has already done most of the same research that you need to do. Use the author's list as a starting point for your own research.