Ethan Couch, 18, nicknamed the "affluenza" teen, was serving 10 years probation for intoxication manslaughter in the 2013 incident.
He and his mother, Tonya Couch, 48, disappeared this month...
At age 16, Couch 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 Good Samaritans who had stopped to help.
Several passengers riding in Couch's vehicle were hurt, including one friend who was permanently brain damaged.
