"She was a 19-year-old little girl, killed in her own home," the victim's stepmother, Carol Lyon, told the defendant in 3rd District Court on Tuesday. "You say you came to this country for a better life is this a better life? Was dealing drugs a better life? You belong in jail."
Arriaga-Luna, 34, was sentenced Tuesday to up to 40 years in prison for slaying 19-year-old Stephanie Williams on Easter in 2010. But he may be deported to Mexico before he is eligible for release.
On Tuesday, he apologized to the girl's family for the first time.
"I just want to say sorry to the family of Stephanie," Arriaga-Luna said through a Spanish interpreter. "I know they have been hurt by this as well as I have been. ... I know I made a mistake."
At first, he didn't feel remorse, his attorney explained.
He believed Williams' boyfriend was going to harm his family his wife and two young daughters. But after his wife was taken into custody and his children removed by the state, Arriaga-Luna said he finally understood what his victim's family had gone through: losing a child.
"He has come to the understanding that this was something he never should have done," defense attorney Brenda Viera said. "The case has cost him personally, and he has begun to understand what he cost Stephanie's family as well."
In a deal with prosecutors, Arriaga-Luna pleaded guilty in December to second-degree felony manslaughter and obstruction of justice and third-degree felony use of a firearm by a restricted person.
He originally faced a murder charge that could have landed him behind bars for up to life.
Tuesday's sentencing was the long-awaited conclusion of a four-year-old case that went all the way to the Utah Supreme Court and back after justices ruled last year that Arriaga-Luna's confession to police was admissible in a trial.
According to court documents, Arriaga-Luna finally admitted to killing Williams after police mentioned the potential for a life sentence, used a "false friend" interrogation technique and brought up the welfare of Arriaga-Luna's daughters.
A district court judge had ruled the confession couldn't be used, given the use of Arriaga-Luna's daughters as a persuasion tactic and called it coercion. But the Supreme Court disagreed.
Stephanie Williams was killed in her Salt Lake City home on April 5, 2010, with two gunshot wounds to the head.
During the investigation, Williams' boyfriend, Victor Manuel Sanchez, told police that Arriaga-Luna was responsible for the killing.
Sanchez later faced kidnapping charges for trying to use Arriaga-Luna's wife as a pawn to get him to surrender. A jury acquitted Sanchez in April 2011 on the basis that Arriaga-Luna's wife cooperated of her own accord.
Sanchez's attorney described Arriaga-Luna as a violent drug dealer determined to collect on his debts.
On Tuesday, the Williams family echoed that sentiment.
"All he ever cared about was the money," said Lacey Williams, the victim's sister. "He took someone so special to us and then showed no remorse. I'm glad he's not getting out for a long time."
She recalled her younger sister as "high-spirited," "the fun one" in the family.
More than a dozen of Stephanie Williams's friends and family attended Arriaga-Luna's sentencing.