Arriaga-Luna's case began April 5, Easter Sunday, 2010, when police found Williams dead from two gunshot wounds to the head. During the investigation, Williams' boyfriend, Victor Manuel Sanchez, told police 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.
Sanchez's attorney has previously described Arriaga-Luna as a violent drug dealer determined to collect on his debts.
Court documents reveal that a day after Williams' slaying, police interviewed Arriaga-Luna and said he should confess so he could continue to see his daughters. Arriaga-Luna refused to admit his alleged role in the killing, the documents explain, but finally confessed two days later after a conversation with a different detective.
The documents say the other detective used the "false friend" technique, making small talk and discussing Arriaga-Luna's love of his daughters. The confession came after the detective mentioned that if Arriaga-Luna confessed, he could tell his daughters he made a mistake but retain his dignity.
Arriaga-Luna's attorneys later argued that bringing up the daughters, among other things, amounted to coercion because it was a veiled threat. However, the Supreme Court ruled that appealing to a defendant's love of his child is not necessarily coercive.
Assistant Attorney General Ryan Tenney, who worked on the case, said Tuesday he was satisfied with the ruling, adding the "court got this one right." The Utah Supreme Court struck a "careful and delicate" balance between what amounts to coercion and what police can discuss, and didn't apply a blanket rule that would completely prohibit an entire topic from interrogations.
That issue previously was "something of an open question" in Utah, Tenney said.
Arriaga-Luna's attorneys did not immediately return calls seeking comment Tuesday.