On a mild spring evening in northern Iraq, Staff Sgt. Martin K. Richburg sat in a flatbed truck parked outside the Internet cafe on base and called his wife back in Baltimore. As Richburg, 44, spoke on his cell phone, he saw an Iraqi civilian place a blue bag atop the cafe's air conditioner and take off running. Richburg drew his 9 mm pistol, chased down the man and prodded the truth from him: The bag contained a bomb. Richburg cleared the cafe where soldiers checked their e-mail, and a few minutes later a blast destroyed the building.