MEXICO CITY (REUTERS) - A wealthy Texas teen who fled with his mother to Mexico to avoid possible jail time for breaking his probation in a fatal drunken-driving crash was captured by Mexican authorities and was likely to be returned to the United States later on Tuesday.

Ethan Couch became known in the United States as the "affluenza" teen during his trial in juvenile court over the deaths of four people in the 2013 crash. A psychologist said in his defence that he was so wealthy and spoiled he could not tell the difference between right and wrong.

Couch has been serving 10 years drug-and-alcohol-free probation for intoxication manslaughter - a sentence that sparked outrage among critics who said he had been lightly punished because of his privilege.

Couch, now 18, and his mother, Tonya Couch, fled the country after a video surfaced online apparently showing Couch at a party where beer was being consumed. Authorities had been investigating that video as a potential parole violation.

Couch had missed a mandatory meeting with his probation officer, prompting officials in Tarrant County, Texas, to issue a warrant for his arrest earlier this month.

Couch and his 48-year-old mother were tracked down in Mexico and taken into custody on Monday evening in the Pacific Ocean beach city of Puerto Vallarta. Mexican authorities said they had been working with the US Marshals Service since Saturday to locate the pair.

The mother and son apparently entered Mexico by land, said Ricardo Vera, a local official for Mexico's National Migration Institute. He said the two did not register when entering Mexico, but it was not clear where they came in.

They were expected to be returned to Houston on a commercial flight later on Tuesday from Jalisco's state capital, Guadalajara, Vera said.

In Texas, Tarrant County Sheriff Dee Anderson said that when the Couches arrived back in the United States, the young man would appear in juvenile court and his mother would be arrested for hindering an apprehension.

"They had planned to disappear," Anderson told a news conference in Fort Worth, Texas. "They even had something that was almost akin to a going-away party before they left town."

Ethan Couch's attorney, Reagan Wynn, said in a statement he had not had the chance to speak with his client and did not expect to be able to until Couch was back in the United States.

"Until we have more information concerning this situation, it would not be prudent for us to make any further public statement," he said.

BLOND TO DARK-HAIRED

Couch and his mother were captured at the crossing of two streets near the popular Malecon, or seafront promenade, in Puerto Vallarta.

A police booking picture from Mexico showed the previously blond Ethan Couch with dark hair. The sheriff said the darker hair suggested Couch was trying to change his appearance.

Tarrant County District Attorney Sharen Wilson said that she expected the judge to hold Couch after his juvenile hearing, and that she hoped it would be in an adult jail.

At a previously scheduled Jan 19 court hearing, Wilson had planned to ask a judge to transfer Couch's case into the adult court system from the juvenile system, putting Couch under stricter supervision and leaving him open to harsher punishment if he violated probation.

If Couch were transferred into the adult system, he could face 120 days in jail for not meeting with his probation officer as required. In the adult system, he would face up to 40 years in prison if he violated probation again after that, Wilson said.

US Marshal Rick Taylor and Anderson declined to say how authorities tracked Couch down, but CNN said the marshals used Couch's mobile phone to track him down.

'HANDS-OFF' PARENTING

At the time of the fatal accident, Couch, then 16, was speeding and had a blood-alcohol level of nearly three times the legal limit when he lost control of his pickup truck and fatally struck a stranded motorist on the side of the road and three people who had stopped to help.

Susan Cloud, a friend of Brian Jennings, one of the four killed in the accident, said she felt conflicted about what should happen to Couch, but wished he had not thrown away his second chance under his probation.

"I feel more negatively towards his mother than I do him," Cloud said. "The parents seem to have a completely hands-off approach."

Sheriff Anderson said last week that the passports for Couch and his mother had been reported missing by the teen's father, who has cooperated with investigators. Fred Couch is divorced from the mother and owns a successful sheet metal business near Fort Worth.

Ethan Couch became known as the "affluenza" teen after the term was used during his trial.

"Affluenza" has been a theory in sociological and psychological circles since the late 1990s to explain the impact of indulgent parenting, where the combination of affluence and indulgence creates a sense of invincibility and lack of accountability in the child, said Daniel Medwed, a criminal law professor at Northeastern University in Boston.

The Couch case appeared to be the first time it was explicitly offered as a defence.

But the notion of rich kids getting leniency based on their advantages sparked a public backlash against the theory, Medwed said.

"My hunch is this latest parole incident will mark the end of its use," he said.