Her daughter had been missing for about a month when Maria Reyes hacked into the 15-year-old’s Facebook account and discovered the death threats.

“Those guys want to kill you,” warned one private message in Spanish. “They have already given permission to take you out.”

“Get ready,” said another.

The profiles of the people making the threats featured skulls, guns, coffins and gang signs that Reyes immediately recognized as emblems of Mara Salvatrucha, better known as MS-13. The 36-year-old had witnessed the street gang’s brutality in El Salvador. And in the summer of 2014, she had sent for her daughter to join her in the United States to escape MS-13.