Detectives Y Bandidos was launched by Publicaciones Herrerias, S.A. (General Manager Ignacio F. Herrerias) in the late 1930s as part of a mini-explosion of pulp fiction publishing in Mexico. At the time Herrerias also published Mujeres Y Deportes, Cuentos Y Novelas, Chamaco, and Novedades. Bandidos reprinted translated English works along side Mexican fiction, and the subtitle "semanario policiaco" suggests they did this weekly. The copying of American Shadow covers without including a Shadow story inside suggests that copyrights were a secondary concern.

Details of known issues
5 out of the six recorded issues below contain 194 saddle-stitched pages plus cover, the other only 130 pages. The paper used is thinner and smoother (better) than that used in American pulp magazines, but not "slick." The cover doesn't seem to be glossy, but it is on a stiffer stock. The magazine is trimmed, but poorly; The trim size is slightly under 5.5"x7.5".

This issue is dated (in roman numerals) May 24, 1937 (a Monday). I could not find an issue number, but it could be #4 or #5. The cover and lead story are adaptated from The Spider's "Death Reign of the Vampire King" (November 1935).
(Click for 125% of original)		El Rey de los Vampiros     by Grant Stockbridge El brillante desaparecido     by Agatha Christie Fuego y sangre by Luis Polanqui Cómo semata by Eulesius El hampa cree en el mal de ojo     by R. G. A. Grun La pupila verde by Sax Rohmer Error macabro by Dorothy Sayers Los diamantes de Boulardeau     by Andrés Lichtenberger La hostería de la muerte     by Pedro Bouchardon La máquina infernal     by Pedro Boileau
This is issue #16, dated August 12, 1937. The cover and lead story are adapted from "Reign of the Snake Men" (December 1936). That story by Emile Tepperman is fourth in a series of Living Pharoah tales, but it is not yet known whether Detectives Y Bandidos reprinted the others before it; The fact that the title was changed to "The Return of the Pharoah.." is encouraging, though.
(Click for 125% of original)		El regreso del Faraón y los leprosos     by Grant Srockbridge [sic] La fabrica de moneda falsa     by Nick Carter El castigo del satiro by Noel Pricot Esta noche, ¡La fortuna!     by Bernardo Nabonne ¡Lo mato con una cerilla!     by Fred Charles Buse Josuah el profeta by Juan Dorsenne El Cofrecillo de Ebano by G.A. Carey Los hombres morenos     by Pierre Boileau El fin de un mesalina     by Juan Castellano El marido de la chiquilla     by Geo Guasco Central Park by Aubrey Smith Drama Campesino by Noel Pricot Muerte Sospechosa by Pol Prille
This issue is dated 1937. The cover appears to be copied from a Phantom Detective pulp, yet there is no Phantom story inside.
(Click for larger)		La venganza de la calavera     by J. Neumann El último aplauso a la artista     by Anthony Field La caída del último jefe de la "Ogpu"     by Marvin Campbell El hombre que estaba muerto     a Saint story by Leslie Charteris El castillo condenado     by Mildred Show Gearson Sangre en las colinas     by Jean Bazal El pasaporte diplomático     by Frederick Bruner La antropófaga blanca     by Andrés G. Block
This issue is also from 1937. The cover is repainted from a well-known Shadow, yet Maxwell Grant is not listed among the authors. Besides the fiction listed below, the issue features a 35-page article on John Dillinger with photos, and another piece on the murder of Henrietta Schmerler.
(Click for larger)		El esqueleto de la capa escarlata     by J. Neumann Los espantosos crímenes de un    loco en libertad by Felipe Artois Cuando la muerte se viste de amarillo     by Arthur L. Zagat "La Isabel" by Augusto Bailly El hombre de los juguetes     a Saint story by Leslie Charteris ¿Suicida? No, asesisnada     by Nick Carter El monje asesino by Abbas Kamel Paseos de medianoche     by Emmanuel Car F. M. R. by Pierre Boileau Los niños desesperados     by Jorge Rathelot Pesadilla by Will Scott
This issue was listed as #56 and dated May 19, 1938 (a Thursday). It is only 130 pages. Here is a second example of a Shadow magazine cover, with no Shadow story accompanying it inside.
(Click for larger)		La sentencia en el espejo     by Austin Weyland Una noche de terror     by Thomas W. Prince ¡Chinta Aznar!     by Antonio B. Quijano Chapopote: ¡Muerte!     by Mirin D. Green El canto de la sirena     by Alfred Brandon
**This last listing from eBay has very specific data in terms of issue numbering and publication date, but it doesn't add up.**
This issue was listed as "#58" dated "April 31, 1938" (before issue #56 and there IS NO April 31). The cover is believed to have been copied from an American Charlie Chan movie poster.
(Click for larger)		Una tragedia en el Ártico     by W. M. Meirer El hombre del ojo fotográfico     by Joe Massal El rescate del muerte     by Harry Read La heroica belleza de Reno     by Hollis B. Fultz El crimen del General Haas     by Nick Carter Los últimos triunfos de Charlie Chan     by Earl Derr Biggers