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Hours after a U.S. Border Patrol agent was shot and killed, and one other was shot and injured, Manuel Padilla, left, U.S. Border Patrol Acting Chief Patrol Agent Tucson Sector, and Jeffrey Self, U.S. Border Protection Joint Field Command Arizona, leave after a news conference at the U.S. Customs and Border Protection Brian A. Terry Border Patrol Station Tuesday, Oct. 2, 2012, in Bisbee, Ariz.(AP Photo/Ross D. Franklin)

Border Patrol agent killing

The head of the U.S. Border Patrol agents'

union says the agent killed last week in a shooting in southern Arizona

apparently opened fire on two colleagues thinking they were armed

smugglers and was killed when they returned fire. (Oct. 8)