Monsters, Mysteries, and Man (Addison-Wesley, 1979)
Bitter Grain (Holloway House, 1980; reissued 1991)
The FBI Plot (Holloway House, 1981)
Mass Murder (Garland, 1988)
Terrorism in the United States and Europe (Garland, 1988)
How to Write Action/Adventure Novels (Writer's Digest, 1989, reissued by The Write Thought 2012)
FBI Most Wanted (Garland, 1989; Dell 1993)
Hunting Humans (Loompanics, 1990; Avon, 1992-93)
Armed and Dangerous (Writer's Digest, 1990)
The Ku Klux Klan (Garland, 1991)
Racial & Religious Violence in America (Garland, 1991)
Raising Hell (Avon, 1993)
Bad Girls Do It! (Loompanics, 1993)
Silent Rage (Dell, 1994)
Daddy Was the Black Dahlia Killer (Pocket Books, 1995)
Killer Cops (Loompanics, 1997)
Waste Land (Pocket Books, 1998)
Holy Homicide (Loompanics, 1998)
Rope (Pocket Books, 1998)
Black Collar Crimes (Loompanics, 1998)
Cop Killers (Loompanics, 1998)
Still at Large (Loompanics, 1998)
The Encyclopedia of Serial Killers (Facts of File, 2000)
Killer Kids (Loompanics, 2000)
Stolen Away (Pocket Books, 2000)
Century of Slaughter (iUniverse, 2000)
The Invisible Empire (University Press of Fla., 2001) [Winner: Rembert Patrick Annual Book Award]
The Encyclopedia of Kidnappings (Facts on File, 2002)
The Encyclopedia of Robberies, Heists and Capers (FoF, 2002)
The FBI Encyclopedia (McFarland, 2003)
The Encyclopedia of Cryptozoology (McFarland, 2005) [Chosen as one of the Outstanding Reference Source, 2006, ALA]
The Encyclopedia of Conpiracies and Conspiracy Theories (Facts on File, 2005)
The FBI and the KKK (McFarland, 2005)
The Ku Klux Klan: A Comprehensive Reference Guide (McFarland, 2006)
Florida's Unexpected Wildlife (University of Florida, 2007) [Chosen as #6 of the Top Ten list of Cryptozoology Books for 2007]
The Encyclopedia of Crime Scene Investigation (Facts on File, 2007)
The Encyclopedia of Serial Killers, Second Edition (Facts on File, 2006)
Strange Indiana Monsters (Schiffer Publishing, 2006)
Criminal Investigations: Serial Killers (Chelsea House, 2008)
Criminal Investigations: Celebrities and Crime (Chelsea House, 2008)
Criminal Investigations: Gangs and Gang Crimes (Chelsea House, 2008)
Criminal Investigations: Unsolved Crimes (Chelsea House, 2008)
Criminal Investigations: Bank Robbery (Chelsea House, 2008)
Gangsters Encyclopedia (Anova Books, 2007)
Ku Klux Klan in Mississippi (McFarland, 2009)
Mr. Mob: The Moe Dalitz Story (McFarland, 2009)
Hidden Animals (Greenwood Press, 2009)
Strange Kentucky Monsters (Schiffer Publishing, 2010)
Strange California Monsters (Schiffer Publishing, 2010)
The Encyclopedia of Unsolved Crimes, 2nd ed (FoF, 2009)
Crime & Criminals (Checkmark, 2010)
Crime-fighting & Crime Prevention (Checkmark, 2010)
Bomb Squad (Checkmark, 2010)
SWAT Teams (Checkmark, 2010)
Texas Rangers (Checkmark, 2010)
US Marshals (Checkmark, 2010)
Chronology of Organized Crime Worldwide (McFarland, 2011)
DEA (Checkmark, 2010)
Giant Snakes (CFZ Press, 2009)
Strange Monsters of the Pacific Northwest (Schiffer Publishing, 2011)
Prison and the Penal System (Checkmark, 2010)
True Crime: Gangsters--Outside the Law (Igloo Books, 2010)
When Bigfoot Attacks (CFZ Press, 2011)
Teabonics (eBook, 2011)
Strange Pennsylvania Monsters (Schiffer, 2012)
Globsters (CFZ Press, 2012)
The Mafia at Apalachin (McFarland, 2011)
Ku Klux Terror (Schiffer, 2013)
Teabonics! (Smashwords, 2011)
Writing Westerns (Writers Digest ebooks, 2012)
So You Want To Be A Writer (eBook, 2012)
Writing Thrillers (Writers Digest ebooks, 2013)
Strange Ohio Monsters (Schiffer, 2013)
Famous Assassinations in World History, and Encyclopedia (ABC-Clio, 2014)
Hoaxed! (CFZ Press, 2013)
The Texarkana "Moonlight Murders" (McFarland, 2014)
Hate Crimes in America: 1968-2013 (McFarland 2014)
White Robes and Burning Crosses (McFarland, 2014)
Seeking Bigfoot (Schiffer, 2015)
Strange West Virginia Monsters (Schiffer, 2015)
Sasquatch Down (CFZ Press, 2015)
The World's Worst Serial Killers (eBook, 2014)
The Dark Strangler: Earle Leonard Nelson (RJ Parker, 2015)
Unsolved Civil Rights Murder Cases, 1934-1970 (McFarland, 2016)
Hangman: The Life and Crimes of Gerard John Schaefer (R.J. Parker, 2016)
The National States Rights Party: A History (McFarland, 2017)
Iron Curtain Killers (RJ Parker, 2017)
Hearts of Darkness (RJ Parker, 2018)
Doctor Death (RJ Parker, 2019)
Boss of Murder: The Criminal Life of Albert Anastasia (Exposit, 2020)
Extreme Killers (Sterling, 2020)
Frankie Yale: Iceman of Brooklyn (Exposit, 2021)*
G-Men
