A retired Marine with nearly two decades of aviation experience has stepped forward with a compelling theory about a mysterious plane that was spotted flying over Texas last month. On March 10, photographers Steve Douglass and Dean Muskett took pictures of three puzzling aircraft flying over Amarillo, and posted them online in hopes of identifying the planes. Retired-Marine James Vineyard has submitted one of the more interesting explanations, telling the Houston Chronicle he believes they are SR-72 Blackbirds - a spy plane that can cross the U.S. in less than an hour, unmanned.