Just 16 years old at the time, Couch and seven other teens piled into the truck after a night of partying and drinking, authorities said.
Couch was barreling down a Burleson, Texas, road at approximately 70 miles an hour, when he lost control, swerved into a ditch and plowed into a group of people who were helping a stranded motorist on the side of the road, authorities said. The crash killed all four people instantly and seriously injured two of the teens in Couch's truck.
But what catapulted the case into the national media was Couch's defense team arguing that the Texas teen suffered from "affluenza" -- a term used to describe Couch's irresponsible lifestyle associated with his affluent upbringing -- and that he should go into rehab instead of serving jail time.
Couch pleaded guilty to four counts of intoxication manslaughter and two counts of intoxication assault on Dec. 4, 2013, followed by three days of testimony to determine his sentence.
That’s when Dr. G. Dick Miller, a prominent psychologist hired as part of the defense legal team retained by Couch’s parents one day after the crash, reportedly testified that Couch was a product of "profoundly dysfunctional" parents who gave their son too much and never taught him the consequences of his actions. Dr. Miller used the term "affluenza" in describing Couch, and said he should be treated at a rehab facility instead of serving a jail term.
"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," Miller reportedly said in court.
According to Miller, Couch grew up learning he should be able to do what he wanted, whenever he wanted and noted that Couch's father Fred Couch made millions of dollars thanks to his successful sheet metal business.
"I think Ethan Couch is suffering from adjustment reaction to adolescence, I would say," Miller said in never-before-seen deposition tapes from a civil lawsuit resulting from the crash obtained by ABC News' "20/20."
For example, Miller testified that Couch's parents allowed him to start driving alone when he was just 13 years old even after a teacher expressed concern.
"[The teacher] said he's not allowed to drive to school," Miller said. "[Couch's father's response was] something to the effect that, 'I'll buy the school,' or something along that line." Couch's parents pulled him out of school and opted for home-schooling.
During his deposition, Miller said that Couch was raised by his parents with "no reasonable boundaries." He reiterated what he reportedly said at the criminal trial that Couch was taught by his parents that if he hurt someone, he could send money.
"He was never safe, and to me, a child needs to be safe from day one. [His parents] had an adversarial relationship, and Ethan was given something to--he was bought a toy in Toys 'R' Us when [his parents] had a fight," Miller said.
Miller said Couch's parents also taught him "to an extent" that others were beneath him and have no worth.
Just four months before the fatal crash, police stopped a drunk 15-year-old Couch at 1 a.m. for relieving himself in a parking lot. Though he was alleged to be in clear violation of five different laws, according to attorney Todd Clement, Couch got away with a summons and was sent home with his mother Tonya Couch.
"It reinforced that indeed the rules don't apply to Ethan Couch," Miller said.
During his deposition, Miller said he had "strongly" recommended in the criminal sentencing that Couch needed to be separated from his parents and that their parenting "strongly enabled" the deadly accident.
Judge Jean Boyd sentenced Couch to 10 years of probation and time in a rehab facility for the fatal accident, a ruling that shocked the victims' families and made national headlines.
The Couches declined ABC News' "20/20" requests for comment.