By Marice Richter

FORT WORTH, Texas (Reuters) - A Texas judge ruled on Friday that America's so-called "affluenza" teenager should remain in custody for now at a juvenile detention center in Fort Worth, where he has been held since he was deported from Mexico on Thursday.

Ethan Couch, 18, fled to Mexico last month with his mother after he apparently violated the probation deal reached in juvenile court that kept him out of prison for killing four people while driving drunk in 2013.

Judge Timothy Menikos said he was considering a move to an adult prison for Couch. If that happens, Couch could be eligible for release on bail, court officials have said, adding the bail option was not available to him in the juvenile system.

Couch faces a hearing on Feb. 19 to determine if his entire case will move to the adult system. He also faces 120 days behind bars if it is found that he violated the probation deal.

Prosecutors want his case moved to the adult system, where he could face 40 years in prison for any subsequent probation violation.

"I have confidence that he cannot abide by the terms of his probation," said Tarrant County prosecutor Richard Alpert after the hearing.

Couch was sentenced to 10 years of drug-and-alcohol-free probation for intoxication manslaughter, a punishment condemned by critics as privilege rewarded with leniency.

"He has never apologized to the victims," Alpert added.

Couch fled to Mexico after a video emerged on social media that appeared to show him at a party where alcohol was being consumed.

Couch was 16 when he was tried as a juvenile. He gained notoriety when a psychiatrist testifying on his behalf said he had "affluenza," arguing that his family's wealth had left him so spoiled that it impaired his ability to tell right from wrong.

The affluenza diagnosis, not recognized by the American Psychiatric Association, was widely ridiculed.

His mother, Tonya Couch, faces up to 10 years in prison for helping her son flee to Mexico.

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Couch's blood alcohol content at the time of the crash, when he killed a stranded motorist and three other people, was nearly three times beyond the legal limit for an adult.

A lawyer for Couch said on Friday he will abide by the terms of his probation.

"Of course Ethan is sorry," the lawyer, Scott Brown told reporters. "Just because he hasn't given a public statement doesn't mean he isn't remorseful."

(Writing by Jon Herskovitz; Editing by Tom Brown)