PHOENIX – Investigators searching a stretch of the U.S.-Mexico border for clues into the fatal shooting of a Border Patrol agent face a treacherous territory that is heavily used by drug smugglers, offers many hiding places and is close enough to Mexico for traffickers to make a quick getaway.

Whoever killed Agent Nicholas Ivie and wounded another agent in the sparsely populated desert in southeastern Arizona early Tuesday may have done just that.

Those who carried out the shooting near Bisbee, Ariz., probably had time to cross the border in the early-morning darkness before authorities could seal off an escape route, said George McCubbin, president of the National Border Patrol Council, a union representing about 17,000 border patrol agents.