A DOCTOR TELLS HOW HE'D KILL HIS EX-WIFE ALL CAUGHT ON VOICE RECORDER, ON "20/20"

Airing Friday, September 18 at 10 pm on ABC

When Joannah started dating Dr. Greg Konrath of Indiana, he appeared to be a great catch - he was a well-respected orthopedic surgeon and author, earning $1.7 million a year, and an accomplished mountain climber. That is until a night of cocktails while on vacation in Puerto Rico when, after a few drinks, Dr. Konrath began telling Joannah about how he would kill his ex-wife as their kids slept in the next room. Shocked, Joannah secretly took out her iPhone and recorded the conversation, complete with how he would shoot his ex in the head with an untraceable gun and then make it look like a suicide.

"20/20" has exclusively obtained the recording and the police interrogation tapes. But in a surprising twist, Konrath is now behind bars for an entirely different crime. ABC News Correspondent Linzie Janis has the first network interview with Dr. Konrath in jail, as well as an interview his ex-girlfriend Joannah, breaking her silence about the case for the first time.

"20/20," airs FRIDAY, SEPTEMBER 18 (10:01-11:00 p.m., ET) on ABC.

"20/20" is anchored by Elizabeth Vargas and David Muir. David Sloan is senior executive producer.