Complex sentence: Tom Golden, a career army intelligence operative detailed to the CIA and assigned to the U.S. Embassy in Montevideo, was a personal friend of Mitrione who worked closely with Uruguayan officials to try to secure the release of Mitrione and prevent his execution.
Split into simpler sentences: Tom Golden, a career army intelligence operative detailed to the CIA and assigned to the U.S. Embassy in Montevideo was a personal friend of Mitrione. Golden worked closely with Uruguayan officials to try to secure the release of Mitrione and prevent his execution.