The mission of the United States Department of Justice is "To enforce the law and defend the interests of the United States according to the law; to ensure public safety against threats foreign and domestic; to provide federal leadership in preventing and controlling crime; to seek just punishment for those guilty of unlawful behavior; and to ensure fair and impartial administration of justice for all Americans."
The website, National Criminal Justice Reference Service differs from the database by the same name. They are both useful. For data, you should explore the Bureau of Justice Statistics site and make use of the data analysis tools and view the data collection and peruse the publication list. Also view the National Archive of Criminal Justice Data.
Most of the documents listed on the list below are on the Alphabetical listing of Publications & Products webpage. In addition to the titles listed below, there are many other useful titles in full-text on this website.