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What to Watch on Friday: 20/20 has the Gerardot love triangle murder-suicide

Mark Gerardot, left, is interviewed by Amy Robach for ABC’s “20/20.”
Mark Gerardot, left, is interviewed by Amy Robach for ABC’s “20/20.” ABC

NOTE: Please be aware that Hurricane Dorian coverage could preempt regular programming on broadcast networks.

20/20 (10 p.m., ABC) - Amy Robach interviews Mark Gerardot, whose wife, Jennair Gerardot, killed Mark’s girlfriend, Meredith Chapman, and then herself in a Philadelphia suburb last year. Jennair had spied on her husband during his affair, even sewing listening devices into his clothing to record his conversations. The program also has interviews with Mark’s best friend, a reporter who covered the case, a divorce coach, detectives and former neighbors of the couple.

Dateline NBC (10 p.m., NBC) - Nightly News anchor Lester Holt spends two nights locked up and embedded inside the largest maximum security prison in America, the notorious Louisiana State Penitentiary known as Angola.

Couples Therapy (10 p.m., Showtime) - In the premiere of this new documentary series, the hidden world of other people’s relationship is unlocked. Therapist Dr. Orna Guralnik deftly guides real couples through the minefield of honest confrontation to reveal real-life struggles and breakthroughs.

Good Talk with Anthony Jeselnik (11 p.m., Comedy Central) - This new interview series has comedian Anthony Jeselnik chatting with fellow comedians about their careers and influences. For tonight’s premiere he talks to Nick Kroll, but other guests this season include Natasha Leggero, Kumail Nanjiani, Tig Notaro, Kristen Schaal and David Spade.

Into the Dark (Hulu) - The final installment of the season is a female coming-of-age story involving several teenage girls who perform a secret ritual at a purity retreat. When one of them begins seeing a supernatural entity, they begin to question whether the demon they have unleashed is more dangerous than their father’s expectations for their sexuality.

Some programming descriptions are provided by networks.