Note: on my website many of the
pictures can not be seen! They are of course present in the cd's;
contact me if you want to purchase them: evert@klaseboer.com.
The forger Henry Flachskamm owned the Standard Stamp Co in St.Louis (USA). He is know for his forgeries of the 1872 issue of Mexico. See also the book "Philatelic Forgers, their Lives and Works' by V.A. Tyler. His address was No. 4 Nicholson Place, St. Louis, but also 923-925 La Salle Street St.Louis (according to his pricelist of 1893).
He apparently had contacts with another famous forger; Francois Fournier, as this letter from Fournier to Flachskamm indicates.