MCALLEN, Tex. — She trembled as she sat on the witness stand. She kept her head down and avoided looking at the man at the defense table only a few feet away.

In the blue-carpeted courtroom in the Texas border city of McAllen, she was identified only by her initials, M.M.U.T. She had come from Honduras, she told the court, and the smugglers who helped her cross the border had placed her with about a dozen other migrants at a stash house near McAllen. The man in charge was known as El Gordo — the Fat One.

When one of the migrant women escaped one morning, El Gordo forced M.M.U.T. to go with him in his truck to search for her, she testified. He drove her to an unoccupied trailer some distance away.