Public records are stored in a variety of databases, many of which can be accessed for free, or a nominal charge.  Private investigators can use these databases to conduct background research for client cases.  Following are miscellaneous research databases, crime databases, legal databases and more.
 

Access to Archival Databases (AAD) AAD is a search engine into some of NARA's holdings of electronic records. Search by person, geographic areas, organizations, or dates. Archival Research Catalog (ARC) ARC is the online catalog of NARA's nationwide holdings. Perform searches using keywords, by location, organization, person, or topics, and for digitized images. Army Manuals and Publications Database - Army technical manuals, field manuals, Army regulations, technical bulletins, and other similar publications to the general public. Searchable database.

Biographical Dictionary	Biographical information on thousands of notable people spanning from present day to ancient times.
Business Profiles And Credit Ratings	Find detailed information about a business, including business size, sales volume, key executives, credit code and more.
Computer Crime Database	A searchable index to the online Computer Crime Database (2900 URLS).
Crime Library	Library of articles including topics such as major crimes, notorious criminals and great crime fighters.
Cults Page	A large amount of information on cults, links and support.
Disinformation	Search service for individuals looking for information on current affairs, politics, new science and the 'hidden information'.
Excite Newstracker	Free web clipping service. Searches over 300 publications.
FBI Research	Research FBI Records and Information
Federal Records Guide	Search NARA's holdings of federal records at a very high level, to identify which record groups may have material relevant to your research topics. This includes records that originated in the executive, judicial, and legislative branches.
Gang Information Database	Searchable database of internet links to gang related information.
Hate Watch	Information about hate groups and offers links to various related sites and material.
Internet Crime Archives	Online crime archives, mostly dealing with serial killers and cults.
Locks, Safes And Security Information DB	Online databases that provide detailed information on locks, safes and other security information.
Microfilm Catalog	Searchable database of NARA's more than 3,000 numbered microfilm publications. The described microfilm include those created by or purchased by NARA for researcher use. Determine which rolls of microfilm may be the most relevant for your research at NARA.
National Security Archive	Independent non-governmental research institute and library. The Archive collects and publishes declassified documents acquired through the Freedom of Information Act (FOIA)
National Sex Offender DB	Searchable database of sex offenders across the nation. Currently quite limited.
Pay Phone Database	Database of thousands of pay phone numbers located throughout the United States and Canada.
The Drug Library	World's largest online library of drug policy and related searchable databases.
Thomas Register Of American Manufacturers	Founded in 1996, the Terrorism Research Center, Inc. (TRC) is an independent institute dedicated to the research of terrorism, information warfare and security, critical infrastructure protection, homeland security, and other issues of low-intensity political violence and gray-area phenomena. The TRC provides realistic training and cutting edge solutions to real world problems.
Watchman Cult Index	Offers an index to cults, occult organizations, new age groups and religious movements.