One 16-year-old drove drunk, ran a red light and crashed into a pregnant woman's car, killing her and her unborn child. Another drunken teenager rammed a pickup truck into a crowd of people assisting a stranded driver, killing four.

Jaime Arellano went to prison. Ethan Couch went free.

The stories of the two Texas teens illustrate how prosecutors' decisions in similar cases can lead to wildly different outcomes. The poor immigrant from Mexico has been behind bars for almost a decade. The white kid with rich parents got 10 years of probation.

Couch lost control as he drove his family's pickup truck back to a party where he and some friends had been playing beer pong and drinking beer that some of them had stolen from Wal-Mart. The vehicle veered into a crowd of people helping the driver on the side of the road. Authorities later estimated that he was going 70 mph in a 40 mph zone.

The crash fatally injured the stranded motorist, a youth minister who stopped to help her and a mother and daughter who came out of their nearby home.

But prosecutors in Fort Worth said they didn't ask to have his case moved to the adult system because they thought the judge would refuse. Instead, he stayed in juvenile court and became infamous for his psychologist's assertion that his wealthy parents coddled him into a sense of irresponsibility the psychologist called "affluenza."

Arellano was charged with intoxication manslaughter and intoxication assault, the same counts against Couch. But prosecutors in Arellano's case moved quickly after his June 2007 crash to send him to adult court. Arellano took a plea deal and got 20 years in prison, where he remains today.

Sending Arellano's case to the adult system opened the door to the kind of punishment many say Couch should have received from the beginning.

Matt Bingham, the Smith County district attorney and head of the office that prosecuted Arellano, declined to comment on Couch's case but said he considered adult prison to be a fair option for any teenager who has killed someone.

Juveniles don't always commit "what people think of as juvenile crimes," Bingham said. "There is an appropriate punishment for what they have done. And the fact that they're 16 years of age doesn't negate that."

Arellano could never have argued he had "affluenza."

Arellano and his family crossed the U.S.-Mexico border illegally two years before the crash and settled in East Texas. He spoke little English and had little knowledge of the court system. Five months before the crash, he dropped out of high school.

Now 24, he spoke to The Associated Press about his case from behind a narrow glass partition at a Texas prison. Wearing a white inmate uniform, he spoke in soft, accented English that he said he learned while in prison.

Arellano had his first beer at 15 and had driven drunk a few times before. His parents tried to stop him from driving under the influence, but he said he wouldn't listen.

"They talked to me way too many times," he said. "But I just didn't want to hear it."

On the night of June 23, 2007, Arellano was driving an SUV through Tyler, about 100 miles east of Dallas, on his way to a party. He had an open beer and several more in a cooler.

Witnesses saw him swerve through the intersection and slam into a Ford Mustang making a left turn ahead, according to police reports.

Driving the Mustang was Martha Mondragon, a 33-year-old woman who was nine months' pregnant. Mondragon and the child she was carrying were killed. Her 6-year-old daughter flew out of her booster seat and through a car window. She was hospitalized and survived.

Prosecutors quickly sought to have Arellano's case moved to adult court, and a judge agreed.

At that point, Arellano faced two choices: a plea deal with the promise of 20 years in prison and possible parole after a decade, or a jury trial in one of the most conservative regions of the United States and the risk of 50 years in prison. He took the plea.

While he once thought he might have gotten probation if he were white, Arellano said he doesn't feel that way today.

"I know it was serious," he said. "It had to happen this way so I could better myself, so I could think better."

Arellano becomes eligible for parole next year. Once released, he expects to be deported to Mexico, where he hopes to work on a ranch.

Couch faces possible detention for violating his probation when he returns to court on Feb. 19. Depending on the judge's ruling, he could get three months in jail and adult probation, which if violated could land him in prison for up to 40 years.

In the juvenile system, intoxication manslaughter cases in Texas over the last decade were just as likely to result in probation as they are detention, according to figures from the Texas Juvenile Justice Department. Juvenile justice experts say the state's juvenile system places more weight on rehabilitation than the adult system, where punishments are tougher.

Since 2005, Texas has prosecuted 38 juveniles for intoxication manslaughter or intoxication assault. Only three were sent to the adult system, and half of all cases resulted in probation of some kind.

Those numbers do not include juveniles who commit similar offenses but might be charged with different crimes or cases not reported by local authorities to the state.

Once juveniles are in detention, it's more likely than not that they will go free when they turn 19. Only 33 percent of all juvenile offenders are sent to adult prison, according to a study of juvenile sentencing conducted by the University of North Texas professor Chad Trulson.

Trulson said a probation sentence for killing four people might seem "absurd" to the average person.

But in the juvenile system, he said, that type of sentence for intoxication manslaughter and potentially more serious offenses "is probably more typical than we would think."