ProPublica's project on presidential pardons benefited from a lawsuit filed in 2008, under the Freedom of Information Act, by George Lardner Jr., a former Washington Post reporter. Lardner's successful suit forced the Justice Department's Office of the Pardon Attorney to make public the names of pardon applicants who had been denied clemency.

Professor P.S. Ruckman Jr., of Rock Valley College, in Rockford, Ill., shared a trove of documents he has collected over the years through Freedom of Information Act requests to the pardon office. Those documents included case jacket covers, which are internal Justice Department tracking notices for pardon applications, and public affairs notices, which until 2008 were issued by the department when someone was pardoned.

The Mintz Group, an investigative services firm, provided invaluable help locating hard-to-find individuals who had applied for pardons.

Experts who reviewed ProPublica's statistical analysis of pardon data include George Woodworth, professor emeritus at the University of Iowa; professor Jack Glaser of the University of California, Berkley; professor Mary Rose of the University of Texas; and professor Richard Rosenfeld at the University of Missouri-St. Louis.

ProPublica's Director of Research Liz Day oversaw research. Researchers include Robin Respaut, Julie Tate, Charles Wilson, Lisa Schwartz, Matt Durning and Joe Kokenge. ProPublica interns Michelle Anderson, Ariel Wittenberg, Ryan Knutson and Sergio Hernandez contributed reporting.