May began as a private detective in Salt Lake City, Utah, shortly after the turn of the century and later established his own agency, the Revelare International Secret Service, which he moved to Seattle, Washington in 1919. Although basically self-taught in scientific matters, May built a solid reputation among police agencies and attorneys in the Pacific Northwest and Western Canada as a serious and effective scientific investigator in the era before public crime laboratories. This reputation as "America's Sherlock Holmes" also led to his being consulted on the establishment of the first American crime laboratory at Northwestern University in Chicago, Illinois and on a laboratory for the Royal Canadian Mounted Police at Regina in Saskatchewan, Canada. He contributed to a landmark case of court acceptance of toolmark identification, invented specialized instruments, and founded an institute to teach scientific criminal investigation to police officers. His earliest associates were John L. Harris and J. Clark Sellers, both of whom became recognized document examiners on the West Coast and were followed by a second and a third generation of practitioners. 9 references and 1 figure (Author abstract)