MISSION, Texas — Esteban Manzanares was working his regular day shift as a U.S. Border Patrol agent along the busiest stretch of Mexican border when a trio of Honduran immigrants spotted him and offered to surrender.

A woman, her teenage daughter and a teenage family friend later told authorities they were taken into custody and driven away from a popular county park just north of the Rio Grande and upriver to a more remote, scrub brush-filled area. It was there, in this rugged no-man’s land between the river and a stretch of rust-covered steel border fence, that the older woman says the group was assaulted by a man wearing green fatigues who left the area with one of the girls.