The night of June 14, 2013, 19-year-old college student Adrienne Salinas helped her two roommates throw a party at their Tempe, Ariz. home for a friend's birthday.

But after getting dolled up for the festivities, her roommate Shainey Duggan says Salinas wasn't in the partying mood.

The unsettling case is the subject of Monday's episode of People Magazine Investigates. Titled "Darkness in the Desert," the episode airs August 15 at 9 p.m. ET on Investigation Discovery and also streams on discovery+. (An exclusive clip is shown below.)

"Adrienne was sitting on her bed alone in the room, all dressed up and ready for the party, but not wanting to join what was going on downstairs," Duggan explains during the episode. "She said she just really wasn't in the party mood that night."

The party raged on into the early morning hours of June 15, and Duggan says things got out of hand.

"At some point, someone broke our TV. Someone took our ottoman out into the front yard and lit it on fire," Duggan says. "For me, it was kind of a blur, kind of a whirlwind. And Adrienne spent a lot of the night with Fran, as far as I understand, so I didn't see her too much that night."

"Fran" or Francisco Arteaga was Salinas' boyfriend.

Duggan also said the couple wasn't getting along that night and that "Adrienne was upset about Fran talking to another girl, or being interested in another girl, and it hurt her feelings."

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That morning was the last time friends and loved ones heard or saw Salinas.

Her abandoned car – which was headed for Fran's house - was located a few blocks away from her home with two blown out tires, but Salinas had mysteriously vanished.

Nearly two months later, her skeletal remains were discovered in a wash about 30 miles away in the Apache Junction desert.

And her killer was on the loose.

See more on the disturbing mystery of the death of the Arizona college student on People Magazine Investigates ("Darkness in the Desert"), airing Monday, August 15, at 9 p.m. ET on Investigation Discovery and also streaming on discovery+.