A 16-year-old Pennsylvania girl and a 45-year-old man were found Mexico on Saturday, March 17, after the pair allegedly ran off together nearly two weeks ago, authorities said.
She and Kevin Esterly, the man police say she willingly ran away with, were escorted to Miami by US Homeland Security Investigations agents and the US Marshals Service.
The teen was unharmed, Amy's mother told the paper.
Yu and Esterly were taken into custody on Saturday morning in Playa del Carmen, Quintana Roo, Mexico, according to Immigration and Customs officials.
Frank Castrovinci told CNN that he observed the pair together and initially thought Yu was Esterly's adopted daughter, before he saw them interacting.
Police issued a missing person alert and filed a warrant for Esterly's arrest.
Allentown police said Friday that Amy and Esterly bought one-way tickets from Philadelphia to Dallas and then headed to Cancun.
Kevin Esterly and his family have known Yu for about eight years, having met through church, according to the Morning Call.
On Sunday, 69 News spoke with a neighbor of Yu's family, the brother of Kevin Esterly, and the attorney for Kevin's wife Stacey, John Waldron.
The police were to be notified if Esterly returned to the school, Mauser said. The mother also discovers that Esterly had signed out her daughter from school at least 10 times.More news: Labour Leader Corbyn Questions Theresa May's Claims
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Amy was reunited with her family.
February 9: Miu Luu, Amy Yu's mother, drives out in the afternoon to pick up her daughter at the Lehigh Valley Academy Charter School, but she's told Amy already has been picked up by Esterly, according to police and Luu.
The case has made headlines in the Lehigh Valley and beyond.
Esterly had also vanished, along with $4,000 he had withdrawn from his wife's bank account.
As details about the relationship trickled out, there were fights over phones that contained a troubling electronic trail.
But during that time, investigators believe, Amy and Esterly were making plans to leave Allentown together. Luu confronts Esterly about the secret pickups and text messages to her daughter, but he calls suspicions about him "lies and speculation", according to Luu.
CNN has reached out to Mexico's attorney general and the federal police for comment, but has not heard back.
Kevin Esterly was angry, John Yu said, and denied his relationship with Amy.
Both were smiling as they were taken into custody - Kevin in handcuffs, Amy in a vehicle.