In the 1930s, Franklin D. Roosevelt gave J. Edgar Hoover unprecedented powers to fight the kidnappings, killings, crime bosses, and criminals that flourished at that time. Hoover countered the magnetism of such crime figures as "Pretty Boy" Floyd, Bonnie Parker and Clyde Barrow, John Dillinger, "Machine Gun" Kelly, and "Baby Face" Nelson with the sometimes graphic photographic images that the FBI used as evidence in court or provided to the press. The wide dissemination of such images was of great propaganda value to the government in its struggles with criminals.

By the mid-1940s, Hoover turned his attention to political radicalism, the incursion of the Left, and the threat of the cold war. FBI photographs of this period focus on suspected informers, spies, and any others deemed to be interested in the destruction of the American way of life.

With the twenty-first century almost upon us, the role of science in criminological investigations has never been more manifest. Evidence pictures are now made using a blinding array of technologies to capture minute and often unseen cluesa shoe print or the residue of a body once wrapped in a sack. The chance existence of latent fingerprints on a murder victim's palm is examined through chemical or microscopic analysis. The turn-of-the-century triumph of fingerprinting over Bertillon's anthropometric measurement system as the crucial method of determining unique physical characteristics has now given way to routine investigations into the genetic material that differentiates one human being from another.