(NBC News) - A Texas teenager famous for invoking an "affluenza" defense while on trial for a fatal drunk-driving crash has been taken into custody in Mexico after weeks on the run, officials said early Tuesday.

Ethan Couch, 18, and his mother Tonya disappeared earlier this month, triggering a manhunt involving the U.S. Marshals and the FBI.

Mexican authorities have been lending support to the search since Friday, according to the Attorney General's office for the state of Jalisco.

It said in a statement that Couch and his mother had been into custody around 6 p.m. on Monday evening in the coastal resort city of Puerto Vallarta and had been handed over to immigration authorities.

The Tarrant County District Attorney's Office also confirmed that Couch and his mother were in Mexican custody, but did not provide further details. It was not immediately clear when Couch would be transferred to the U.S.

Couch has been on the run since earlier this month; flags went up after he missed an appointment with his probation officer.

Officials went to the house where he was allegedly staying with his mom, and found the place empty — save for a pinball machine, according to Reuters.

Tonya Couch's mother also grew concerned over the pair's whereabouts and contacted the sheriff's office to report her as a missing person.

Earlier this month, a brief video emerged on Twitter of young men playing beer pong. The person who posted the video claimed Couch — who cannot drink or use drugs and drive — was in the video and was violating his court terms. The Tarrant County district attorney has said the office was investigating the claim.

Couch met with his probation officer around the time the video surfaced, but didn't return after that, Reuters reported.

Tarrant County Sheriff Dee Anderson previously had told NBC News that he was "not surprised at all" that Couch ran, saying he believed Couch and his mother had fled the country.

Couch admitted to the 2013 fatal drunk-driving crash but did not get any jail time, thanks in part to an unusual defense strategy: A psychologist who testified on the wealthy teen's behalf said Couch was afflicted with "affluenza," which made him unable to distinguish right from wrong due to his privileged upbringing.

Affluenza is not recognized by the American Psychiatric Association as an official diagnosis.

At the time of the crash, Couch was 16 and had a blood-alcohol level nearly three times the legal limit. He received 10 years of probation and orders to go to a rehab center.