Plot Synopsis

SOMEONE YOU THOUGHT YOU KNEW is a one-hour documentary series that chronicles true-life murder cases, where the victim knows the killer -- but maybe not as well as they thought. In homicide cases, it's seldom strangers you need to worry about, it's those closest to you. Even when the killing appears to be random, there can be something more sinister lying beneath the surface: a calculated plot, set in motion by someone close; someone hiding in plain sight; or someone leading a double life. In the series opener, "Killer Collection," Gary and Jan Tyrrell are a beloved couple living in a quaint suburb of Springfield, Missouri. The tight-knit community is soon rocked by their double homicide, with friends and neighbors looking at those closest to the pair as their potential killer.
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On Thursday, September 6, 2018 at 10pm ET/PT, Investigation Discovery premiered the season finale of SOMEONE YOU THOUGHT YOU KNEW. In the season ender, "Pick Your Poison," Bill and Mary Yoder are a happy couple, running a medical practice outside of Utica, New York. But their world collapses when Mary becomes mysteriously sick, and detectives prove that her illness was no accident.