Federal Bureau of Investigation. "Herman Hollis". fbi.gov. Retrieved August 4, 2011.
vault.fbi.gov
Hoover, J. Edgar. "Melvin Purvis Part 02 of 03"(PDF). FBI Records: The Vault. Federal Bureau of Investigation. p. 209. Archived from the original on May 14, 2019. Retrieved December 26, 2023.
Wallis, Michael. "Floyd, Charles Arthur (1904–1934)". Encyclopedia of Oklahoma History and Culture. Oklahoma Historical Society. Retrieved October 27, 2010.
Hoover, J. Edgar. "Melvin Purvis Part 02 of 03"(PDF). FBI Records: The Vault. Federal Bureau of Investigation. p. 209. Archived from the original on May 14, 2019. Retrieved December 26, 2023.