During the summer of 1861, Thomas Killen, William Washington, and Sowell, hunting stock on Poe Prairie, north of Millsap in Parker County, stopped in the shade to let their horses graze. Each of them were unarmed and suddenly charged by about eight Indians.
Killen received a mortal wound and Washington was seriously wounded. All three, however, escaped. But Thomas Killen died six weeks later and was buried in the Rock Mill Graveyard.
Ref: James Newberry who lived in that portion of Parker County at the time.
The above story is from the book, The West Texas Frontier, by Joseph Carroll McConnell.
The following second version is from the book, Indian Depredations in Texas, by J.W. Wilbarger.