Don Borelli, COO, Soufan Group
Paul Keim, Cowden Endowed Chair of Microbiology, Northern Arizona University
Malcolm Brady, former assistant director of the Bureau of Alcohol, Firearms and Explosives
Explosions at the Boston Marathon, potentially ricin-laced letters intercepted en route to the White House and Sen. Roger Wicker, and an explosion at a fertilizer plant in Texas have each prompted investigations. In each case, authorities sift through evidence to construct a timeline of events.