Lee, Zack: I've done some sleuthing this morning based on the Bradley County book I mentioned, it appears the guerrilla was John Gatewood, son of Pemberton Gatewood (1808-1902) of Fentress County, TN, and later Johnson Co., TX, who died in Ennis TX, and his wife Nancy Rhea. This John married Mary Amelia Shumate (b. 1851 Dadeville, AL) and had a daughter Emma Blount Gatewood (born 1874 Smith Co., TX, died 1940 Houston, married John C. Wright and has descendants). Pemberton had son Abner Lytle, b. Dec. 1854, with whom he lived in Johnson Co. in 1880. It appears most of the extended Gatewood clan moved to Johnson Co. in the early 1870s.

If this "informed conjecture" is correct, John P.'s middle name would likely be Pemberton (after his father) or Pleasant (after his cousin).