Kilmar Armando Abrego Garcia, all of 16, called his older brother in distant Maryland with startling news. He had made it to the Texas border. He had escaped.

In his family’s telling, this is how his American journey began. They say that for years in El Salvador, a gang called Barrio 18 had terrorized them, extorting money from the mother’s small tortilla and pupusa business, threatening to leave them all dead in a ditch — and targeting young Kilmar, in and out of school, with increasing menace.

“‘They will appear in black bags,’” his mother said through tears, recalling phone messages from the gang. “Those were the words they would say.”

Seeing a dim future, the teenager had slipped away to follow the worn, treacherous path known to so many other migrants before him, including his older brother. North, across desert and river, into Mexico, and then into the United States.

Over the next dozen years, Mr. Abrego Garcia would call Maryland his home. He would work in construction. Marry. Help to raise three children, all with special needs. He would also be repeatedly accused by his wife of verbal and physical abuse — and be labeled as a gang member by the president of the United States.

On March 15, the tumultuous American journey of Mr. Abrego Garcia returned him to South Texas, in restraints. There, on the tarmac of Harlingen Airport, loomed three large airplanes bound for El Salvador.