Stephanie Leutert, a prominent migration expert at the University of Texas at Austin, has been to a lot of hot spots along the U.S. Mexico border — and even deeper south on Mexico’s dicey frontier with Guatemala.

But nothing prepared her for the scene that played out on an international bridge connecting Mexico and Texas on Friday afternoon, when she says a high-ranking U.S. border official sent her back into Piedras Negras — straight into the arms of Mexican authorities who were openly and aggressively threatening to arrest her and two associates from the university.

Their alleged crime: escorting a 15-year-old Salvadoran boy named Leonel — left alone after his single mom died — to the midway point of the bridge so he could seek asylum in Eagle Pass, Texas.

Over the next hour, Leutert and two UT researchers said Mexican officials repeatedly told them that they had “committed a crime” and would be arrested, and that the boy had no right to be in Mexico and would be taken into their custody.

What the Mexican authorities apparently didn’t know is that the office of U.S. Rep. Will Hurd, R-Helotes, had gotten involved and had already reached out to U.S. authorities. Also furiously trying to help Leutert and her crew behind the scenes were the American Civil Liberties Union and a pro-immigrant group assisting Leonel.

Neither Hurd nor his spokeswoman immediately responded to calls and messages seeking comment for this article.

As Leutert and her associates waited in the offices of the National Migration Institute, a high-ranking Mexican city official — who had earlier told Leutert over the phone she had engaged in human smuggling and other crimes — called her back, Leutert said.

In an agitated tone, the city official, Hector Menchaca, asked her if the boy she was escorting was the one who had prompted all the “calls from Washington.” She said it was.

“Why didn’t you tell me!” Menchaca demanded, according to Leutert.

Suddenly everyone’s demeanor changed — and minutes later the Americans were again walking toward the U.S. with the boy in tow, hoping for smoother sailing on the bridge.

Immigration advocates and civil rights groups have complained for months that unaccompanied minors are getting stranded in Mexico, subjected to abuse, shakedowns and kidnapping, despite repeated assurances from U.S. authorities that these children are their highest priority for asylum processing.

Still, Leutert didn’t figure she would be at the center of an international standoff when she agreed a few days ago to help out an unaccompanied minor from El Salvador after advocates told her he had been refused entry at another part of the Texas-Mexico border.

A Nogales, Arizona-based group called the Kino Border Initiative was trying to assist the Salvadoran boy, whose older brother lives in Chicago, and Leutert was on her way to visit several Texas border cities to study the ever-changing asylum processes in cities on both sides of the Texas-Mexico border. So she agreed to try to help him once she got to Piedras Negras, just across the Rio Grande from Eagle Pass, roughly three hours southwest of San Antonio.

The saga began at about 3:30 p.m. on Friday, when the trio of UT migration researchers — Leutert, Catherine “Ellie” Ezzell and Jake Dizard — met the Salvadoran teen at a plaza in Piedras Negras. He told them that U.S. authorities in Laredo refused to admit him three days earlier and had instructed him instead to seek asylum in Mexico. The UT researchers told Leonel they would walk with him to the spot on the bridge where U.S. officials are stationed, and then help him navigate what was supposed to be a smooth process.

At first, things went as expected. They reached the midway point of the bridge, and the Salvadoran boy stepped forward and said he wanted asylum in the United States. Then U.S. Customs and Border Protection (CBP) officers stationed there asked to see the researchers’ passports and were told they could enter the U.S, but Leutert and her colleagues said they planned to return to the Mexican side.

But while one of the CBP officers called a supervisor, Mexican security guards showed up, eventually surrounding the three UT researchers. That’s when things grew tense. The guards said that there was a waiting list and process to follow for migrants and that the Salvadoran boy had no right to be in Mexico. And they told Leutert they all could be charged with human smuggling for helping him.

Soon, a city official (not Menchaca) dressed in a brown shirt showed up and told them flatly they were breaking the law and warned: “This is your last chance to avoid arrest.”

Finally a CBP supervisor whose last name was Fuller arrived and, with the Mexican guards present and the city official still loudly threatening to detain the UT group, Leutert asked him: “Are you going to let them arrest us for human smuggling?”

“I’m not going to let you in,” he told her, all three researchers recall. “They are taking you back to Mexico.” Leutert said she later dictated the supervisor's exact words into Ezzell’s phone so she would not forget them.

She also won’t soon forget what one of the Mexican security guards told her on the walk back to Mexico, where they were told they would be arrested: “Things have changed under Trump,” the guard said. “The United States just denied entry to American citizens.

That’s when Leutert fired off calls and texts to Shaw Drake, policy counsel for the ACLU Border Rights Center, informing him that her group had been sent back to Mexico in the company of agents who were threatening to arrest them.

Drake, in turn, said he called Hurd, who made inquiries with CBP. Drake said it was “not only rare, it’s completely illegal” for border guards to refuse entry into the country to its own citizens.

“This incident is an illustration of the unfettered and unsupervised power that this agency feels that it has — that a supervising officer would feel so emboldened as to deny entry to United States citizens, especially in a moment when it was clear to the U.S. officials that Mexican authorities were going to be arresting these U.S. citizens on some sort of charge of trafficking,” Drake said.

In an emailed statement, CBP spokeswoman Margie Garza said the U.S. Privacy Act precludes the agency from "discussing the processing of specific individuals or details regarding to their interaction with CBP."

"If a traveler has a complaint regarding their treatment, they can ask to speak to a supervisor or to a passenger service manager," Garza added.

Menchaca, the city official who Leutert said threatened to arrest them, confirmed that CBP’s Eagle Pass port director, Paul del Rincon, told him in a telephone call after the researchers were escorted back to Mexico on Friday that CBP would take the minor child right away. That cleared the way for them to escort Leonel back to the bridge.

Menchaca also said that he informed Leutert she was not doing things “in the right way” — that the minor did not have legal status in Mexico and should have been processed there first — but he denied threatening her with arrest.

Leutert’s two UT colleagues both confirmed Mexican authorities threatened them all multiple times with arrest on human smuggling charges.

The second escort attempt went a lot better. At roughly 5:15 p.m., Leutert, Dizard and Ezzell returned to the bridge with the young Salvadoran and approached two new CBP officers, who were then stationed at the midpoint of the bridge.

They again were told to wait while the same supervisor showed up, this time with a different solution: instead of sending the researchers and the unaccompanied minor back to Mexico, they would take him into custody and process his asylum claim, the supervisor said.

At that point, the CBP officers at the midpoint of the bridge overheard Leutert asking the ACLU lawyer on the phone if she should write down their names, so they removed their Velcro name tags from their shirts, the three researchers said.

When Leutert inquired about it, the officers told her: “You don’t need to know our names just like we don’t need to know yours.”

I said ‘why?’ Leutert recalled. “And they said, 'We are the federal law enforcement officers, we ask the questions.' ”

A few minutes later — Leonel having disappeared into the bowels of the asylum bureaucracy — all the tension was gone, according to accounts by all three UT researchers.

Leutert and her colleagues suddenly found themselves inside the air-conditioned offices of the Eagle Pass port of entry, back in the U.S., where they were offered water and cookies and got a friendly visit from Del Rincon, the port director.

He told them there must have been some big mixup, that they were expecting the boy on Saturday instead, and that the presence of Mexican authorities on the bridge probably confused the supervisor, the UT researchers said.

Del Rincon pointed out that he had spent $120 of his money to buy toys for migrant children and he said it was “instilled” in every CBP agent to let unaccompanied children enter the port “without problem.”

“We bend over backwards here for these kids,” he told them.

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