Updated 10:26 a.m. ET, Wednesday -- A reporter with the Fort Worth Star-Telegram tweeted that Tarrant County Sheriff Dee Anderson says Ethan Couch will not be returned to the U.S. today. His legal team has filed a motion to keep him in Mexico.

Updated 11:25 ET -- Tarrant County Sheriff Dee Anderson said Ethan Couch and his mother Tonya Couch threw something "akin to a going away party" before the pair fled the country.

In a news conference Tuesday, Anderson said investigators received information on Christmas Eve that helped them pinpoint the Puerto Vallarta area, where they were later detained by Mexican authorities. Ethan and his mother are still in Mexico.

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Texas authorities are working to bring them back to the U.S., at which point Ethan Couch will be taken into custody in a juvenile facility and appear before a juvenile judge. The district attorney plans to pursue efforts to move his case to adult court.

An arrest warrant has been issued for Tonya Couch. Anderson said there is no information that the 18-year-old's father had any knowledge that the two planned to flee.

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Original story - Ethan Couch and his mother Tonya Couch have been detained by authorities in the resort town of Puerto Vallarta, Mexico, the Tarrant County Texas district attorneys office confirmed Monday night.

Couch was 16 when he drove into four people who were gathered around a stalled automobile in Texas in 2013, killing them and seriously wounding two others who were passengers in his truck. He was intoxicated at the time. Couch was sentenced to 10 years probation.

When he failed to report to his probation officer earlier this month, a warrant was issued for his arrest. Authorities suspected he was traveling with his mother.

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Ethan Couch is alleged to have skipped out on probation after a video surfaced on social media that appeared to show him clapping at a party where alcohol was being served, a violation of his probation. U.S. Marshalls joined the search for Couch and his mother on Dec. 18.

During his trial, a psychologist testifying in his defense said the teen suffered from "affluenza" due to his privileged upbringing.

He is expected to be turned over to U.S. authorities.