Mexican police believe that snipers who fired on a three-member Rio Grande rafting party, killing one, were drug traffickers who resented the Americans' unwitting intrusion into a drug deal.

U.S. and Chihuahua state police searched the rugged area Monday and enlisted a top tracker to find the attackers who killed Michael Heffley, 40, as he tried to drag his wounded wife, Jamie, 32, to safety.Police have not identified suspects or made any arrests in the attack, which occurred Saturday on the southwestern Texas border between the United States and Mexico.

Authorities later discovered tracks that indicated the assailants fled on horses toward a Mexican town about 15 miles from the shooting scene.