Missouri mom Diane Staudte had four children. But Rachel, her second youngest, seemed to be her favorite.
The two frequently traded shout-outs on Facebook and shared a mutual love of music. Diane had played the organ at Redeemer Lutheran Church in their hometown of Springfield, Missouri, for 30 years. Rachel, who played the flute, often performed with her.
“They were close,” says Rob Mancuso, who played in a blues band with Diane’s husband and Rachel’s father, Mark Staudte.
The pair grew closer when tragedy struck the family in 2012: That Easter, Diane said she found Mark, 61, dead in bed after suffering from flu-like symptoms for a few days, according to police.
Five months later came more tragedy, when Diane found her 26-year-old son, Shaun, dead on the floor of his bedroom after he said he felt sick, according to authorities.
“We just thought it was a spate of bad luck,” Mark’s brother, Michael Staudte, tells PEOPLE in this week’s issue, on newsstands Friday.
Michael and others say they were shocked when Diane’s second oldest child, Sarah, then 24, was hospitalized the following June. She had flu-like symptoms that turned out to be organ failure.
“We couldn’t believe it,” says Charles Alexander, Mark’s longtime friend and bandmate.
The truth was far more sinister.
Shortly after Sarah’s hospitalization, Diane was charged with murdering her husband and son and trying to kill Sarah. She confessed to putting antifreeze in their drinks as a result of deep animosity toward her family, police say.
• For much more on the Missouri antifreeze murders, pick up this week’s issue of PEOPLE, on newsstands Friday.
In a further twist, when Springfield police detective Neal McAmis questioned Rachel, she admitted to helping her mother poison her father, brother and sister.
Rachel was arrested the day after her mother. Both pleaded to the murders and the assault on Sarah, in a scheme that shook the town. (Diane entered an Alford plea, which acknowledges that prosecutors had enough evidence to convict her without admitting guilt.)
Earlier this year, Diane was sentenced to life in prison without parole. Rachel, who agreed to testify against her mother, was sentenced in March to two life terms, but she is eligible for parole after 42 and a half years.
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Both mother and daughter have since filed motions to vacate their pleas. (Their lawyers declined comment, citing the pending motions.)
Meanwhile, their family and community are left coping with their crimes.
As detective McAmis tells PEOPLE in this week’s issue, “Things like this aren’t supposed to happen in Springfield.”