Please see "The War in Mexico" by Anton Adams (Emperor's Press, Chicago, 1998): Plate 8, Commentary on Plates, p. 179 and the chapters on the Mexican Army and Mexican Army Uniforms.
Also of interest is "The Mexican American War, 1846-1848" by Ron Field (Brassey's History of Uniforms, Brassey's (UK) Ltd., 1997): Part 2, pp. 126-7 and 132-133.
The Gilder Lehrman Collection at the Morgan Library, 29 East 36th St., NY, NY 10016-3403 has, in its collection of documents relating to American History, US Army orders regarding the execution of these men. A point of contact is Ms. Leslie Fields.
I can provide you images via e-mail if you desire.
James B. Ronan II
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