Special Agent Skip Wheeler, Air Force Office of Special Investigations Detachment 438, and Capt. Timothy Brathwaite, 71st Medical Group bioenvironmental engineering, walk a grid and mark evidence during an exercise April 15 at Vance Air Force Base, Okla., on how to preserve and process a chemical or weapon-of-mass-destruction scene that may be a result of criminal activity. (U.S. Air Force photo/Capt. Tony Wickman)