"King Keene, Ninth U. S. Secret Service Corps," is evidently a pseudonym. "Lieut. Keene" was a pen name of St. George Rathbone, but I do not know that he used King Keene.
Items with "Keene, King" as Credited AuthorBlue-Light Bill, the Sapphire Sport; or, The Denver Detective's Lone Hand (1 edition)
Don Danton, the Gent from Denver; or, The Kickup at Kickapoo (1 edition)