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Oct. 29: 'The Night Brianna Vanished', 'Deadly Triangle'

Dateline NBC tells the story of Brianna Denison, who disappeared from her friend's house during the night in January 2008 and was later found dead. Josh Mankiewicz reports on the how the police solved her case with the help of DNA evidence and an anonymous tip.

Watch a preview below for 'The Night Brianna Vanished' at 9pm/8c on Friday:

A love triangle turns deadly when an Air Force Captain is shot dead, and police are left to question his wife and her lover, an Army sharpshooter. Keith Morrison reports on the evolving case that ended in both of their arrests, and the questions that remain unanswered.

Watch a preview below for 'Deadly Triangle' at 9pm/8c on Friday::