Federal and local agencies continued searching Friday for a rich Texas teenager described as having "affluenza" while on trial for killing four people in a drunk-driving crash in 2013.
Ethan Couch, 18, was placed on Tarrant County's most wanted list after his parole officer wasn't able to reach him or his mother Tanya, with whom he lives. On Thursday afternoon, U.S. Marshals and the FBI joined the search, officials said.
Tarrant County Sheriff Dee Anderson told CNN's "AC 360" Thursday evening he "wouldn't be surprised" if Couch and his mother had fled the country.
"My gut feeling says they've gone a long way. They have the money, they have the ability to disappear," the sheriff said. "I don't believe they're the kind of people who would have run a short distance. I believe they planned this."
Terry Grisham, a spokesman for the Tarrant County's sheriff's office, told NBC News on Friday that officials expected the search to take a long time, "unless we get a real lucky break."
"He is a priority," Grisham said. "We're not on a timetable. We're going to take as long as it takes."
The sheriff's office started searching for Couch after he missed an appointment with his probation officer on Tuesday. 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.
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 district attorney says it is investigating the claim, but would not confirm that Couch was in the video.
Couch met with his probation officer around the time the video surfaced, but didn't return after that, Reuters reported.
"I wasn't surprised at all that he ran," the sheriff told CNN, adding that he had been "expecting something like this."
A directive to apprehend Couch has been entered into a national database for law enforcement officers, NBC Dallas-Fort Worth reported.
Grisham said officials have been interviewing people every day to try to get information on where Couch is.
"We will follow every lead as far as we can take it," he said.
Couch admitted to the 2013 crash but didn't 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.
"I'm frustrated," Anderson said Thursday. "To have done what he did, take four innocent lives, impact those families in a way that none of us can fathom and never once express any sentiment of remorse, never ever had any guilt feelings or bad feelings — it was all about him, what could he do to get out of it?"
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.
"We're not going to give up. We're going to come after you," Anderson said.
This article originally appeared on NBCNews.com.