On the night of December 6, 1991, in Austin, Texas, four teenage girls were murdered in a yogurt shop after closing up for the day. The person (or persons) who committed the crime has still not been caught. HBO’s The Yogurt Shop Murders, a four-part documentary, centers around the grief of the victims’ families. “We don’t hear those stories because those people are so traumatized,” explains Barbara Ayres-Wilson, the mother of the two sisters who were killed. The documentary examines the history of this cold case: a defendant put on death row on the basis of a false confession, the attempted murder of a police officer by one of the original defendants, and the relapse of the case into mystery. —Jimmy Lux Fox