(NewsNation) — A new HBO documentary revisits a more than 30-year-old cold case and the hope of investigators that new DNA techniques can finally solve the murders of four teenage girls.

What are the yogurt shop murders?

In December of 1991, firefighters responded to a fire at an "I Can't Believe It's Yogurt" shop in Austin, Texas. When the fire was extinguished, they found the bodies of four teenage girls who had been bound and shot.

On the evening of December 6, 1991, Eliza Thomas, 17, and Jennifer Harbison, 17, were working at the yogurt shop, while Jennifer's sister, Sarah, 15, was in the shop with her friend, Amy Ayers, 13.

Investigators still don't know what happened between that evening and when the fire was found by a patrol officer just before midnight.

The girls had been str

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