My cousin the gangster: how to navigate among too many sources?

Frank Frost a.k.a. Frank Foster was a real Chicago gangster who first worked for the Northside gang under Bugs Moran and moved up to south siders under the infamous, Al Capone. While starting with family lore, the facts need to be verified through outside sources. In this case, the problem was not too little information but too much. How to you sort through the scads of information in newspapers, books, and websites and determine which is the truth and which is "speculation and guesswork".