Authorities are still searching for a troubled Texas teen who may have violated his probation after killing four people in a 2013 drunken-driving accident — and they now fear he may have skipped town.

After Ethan Couch crashed his pickup truck at more than 65 mph into a group of people who had stopped to help a stranded motorist, he was sentenced to drug-and-alcohol-free probation and time in a rehabilitation center. But following the emergence this month of a video claiming to show 18-year-old Couch playing beer pong, authorities launched an investigation to determine whether it was the “affluenza” teen.

Authorities are also trying to determine where he is and are worried he may have left the country.

“With the wealth and the wherewithal that his family has, it’s going to be a tough assignment for us to find him,” Tarrant County Sheriff Dee Anderson said, according to the Dallas Morning News.

The U.S. Marshals Service has joined the search for Couch, who is now considered a fugitive. The FBI has been in contact with local authorities to see how the agency can assist.

“If we [had] a top 10 wanted list today, he’s number one,” Anderson told ABC News.

In June 2013, Couch, then 16, was driving his friends down a two-lane road in Fort Worth when he crashed into a car on the side of the road, according to the Associated Press. Authorities said his blood-alcohol level was three times the legal limit and that he had traces of Valium in his system. Four people were killed, and two teens who were in Couch’s truck were seriously injured.

Couch pleaded guilty to manslaughter and assault while intoxicated.

Couch’s family is reported to be worth millions, thanks in part to a booming sheet metal business. It’s their success — and the way they have handled it — that Couch’s attorneys argue contributed to his reckless behavior.

At trial, his psychologist argued that Couch suffered from “affluenza.”

“Instead of the golden rule, which was ‘do unto others as you would have them do unto you,’ [Couch] was taught we have the gold, we make the rules at the Couch household,” G. Dick Miller testified in court, according to ABC News.

For instance, Miller said, at age 13 Couch was allowed to drive himself to school. When a teacher objected, Miller said, the boy’s father replied, “‘I’ll buy the school,’ or something along that line,” according to the network. His parents ultimately opted to pull him out and home-school him.

“He was never safe, and to me, a child needs to be safe from day one,” Miller said, according to ABC News.

Miller said Couch’s parents “had an adversarial relationship” and that every time they had a fight, they took him to Toys “R” Us and tried to buy his happiness.

Authorities said Couch’s parents have divorced and that his father, who has been working with police during the investigation, lives in Keller while his mother lives near Eagle Mountain Lake, an affluent area not far from Fort Worth.

Still, the teen’s light sentence evoked anger across the country.

The recent emergence of the video put Couch back into the news at a time when he was on authorities’ most-wanted list.

“It’s one of those times when you hate to say ‘I told you so,’ but I told you so,” Sheriff Anderson told the Dallas Morning News. “I knew he was going to end up in more trouble.”

The Tarrant County District Attorney’s Office had filed a motion last month to have Couch’s case moved from juvenile court to adult court when he turns 19 next year, Sam Jordan, a spokeswoman for the office, told The Washington Post. Under Texas law, when someone under 17 is convicted of a crime, the case remains in juvenile court until his 19th birthday, and then the sentence can be dropped.

Couch was sentenced to 10 years of probation, which, in his case, would go away when he turns 19 next year.

“We think he should have been in the adult system already,” Jordan said, “so we applied to have the case moved, meaning he would have to serve the remaining eight years of his probation.”

A judge is expected to rule on the request next year, Jordan said.

“Unfortunately, it’s not something that can be done in absentia,” she said. “He has to be at the hearing.”

Terry Grisham, a spokesman for the Tarrant County Sheriff’s Office, said that until Couch has been found, the motion to move his case cannot proceed.

“As long as he is on the run, he will be a juvenile forever,” he said.

Couch’s attorneys could not immediately be reached for comment.

Authorities said they are at a disadvantage because Couch got a “head start.” He failed to show up for a routine probation meeting Dec. 10, according to the District Attorney’s Office. When an officer went to check on him, he was gone. Authorities issued a warrant last week to take the teen into custody.

About the same time, the party video started to surface on social media, showing a young man who resembles Couch engaging in a beer pong game. Jordan, with the prosecutor’s office, said that “we’ve certainly had witnesses who said it was him” but that “there’s no DNA for video.”

Authorities do not yet have proof that the man in the video was Couch.

When asked whether authorities believe Couch fled to avoid repercussions for a possible probation violation, Jordan said: “It’s certainly suspicious timing.”

Authorities said Couch is not currently wanted for a crime.

Still, Couch’s name has be entered into a database for fugitives, so any U.S. law enforcement officer who finds him can hold him for extradition, said Grisham, the sheriff’s office spokesman.

“Every person who carries a badge in the United States of America is aware he’s a fugitive,” he said, adding: “We have to be prepared for the long haul but ready to move at a moment’s notice.”

Authorities are chasing leads both nationally and internationally.

“You can run, but you’re always going to be looking over your shoulder,” the sheriff said of Couch, according to CNN. “We’re not going to give up. We’re going to come after you. We’re going to find you, wherever you are.”

This story has been updated.