Diane Staudte and her daughter Rachel plotted to poison their family — and they were caught after their concerned pastor tipped off police

Diane Staudte and her daughter Rachel methodically plotted to poison their closest relatives — and they might have gotten away with murder if the pastor of their church hadn’t tipped off police.

His anonymous alert came after months of apparent misfortune for the Staudte family, as first Diane’s husband and then her son fell ill and died. Next, one of her daughters was hospitalized.

But where others in the community were shocked and saddened, her pastor became suspicious.

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It all started when Diane’s husband, 61-year-old Mark Staudte, died on Easter Sunday in 2012. The cause of death was ruled natural causes. Friends and family tell PEOPLE they were struck by the lack of emotion the longtime Springfield, Missouri, resident displayed over the death of the man she had known more than half her life.

During a gathering after Mark’s memorial service, “It was like she was hosting a party,” says Rob Mancuso, Mark’s friend and band mate. “There was no sadness. I thought it was just her way of grieving.”

Diane again showed little emotion when her 26-year-old son Shaun, who she said had suffered from seizures, died five months later of what the medical examiner ruled prior medical causes.

Like his father, Shaun had complained of flu-like symptoms in the days leading up to his death. This time, there was no memorial service, Mark’s brother, Michael Staudte, tells PEOPLE in this week’s issue.

“We found out he died from another relative,” he says.

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Courtesy Staudte Family
| Credit: Courtesy Staudte Family

Those who knew the Staudtes say they were taken aback when Rachel posted on Facebook, “Don’t think I’ve seen mom so chilled out like this in a long time” – exactly one month after Shaun died.

But tragedy struck again the following June, when Diane’s daughter Sarah, then 24, was admitted to the hospital with flu-like symptoms that turned out to be organ failure.

While most people said they couldn’t believe the family’s misfortune, at least one person questioned it, Springfield police detective Neal McAmis tells PEOPLE. Shortly after Sarah was hospitalized in June 2013, an anonymous tipster called police, saying he thought Diane may have murdered her husband and son.

The tipster, McAmis says, turned out to be the pastor of Diane’s church. (The pastor declined to comment.)

McAmis says that when spoke to the pastor, “He talked about Diane’s lack of emotion when Mark died. He thought Diane’s reaction after Mark died was odd.”

The pastor — who told McAmis that he and Mark were friendly and would go out for coffee once a month to talk and catch up — “knew of nothing that would cause Mark to suddenly die,” McAmis says.

“But then, after Shaun, a healthy young man died, that’s when he saw a total lack of emotion and really started to become suspicious.”

diane staudte
Women’s Eastern Reception Diagnostic Correctional Center
| Credit: Women's Eastern Reception Diagnostic orrectional Center

Shortly after Sarah’s hospitalization, Diane was arrested and charged with murdering her husband and son and trying to kill Sarah. She confessed to putting antifreeze in their drinks, according to court records, which further show that when McAmis questioned Rachel, she admitted to helping her mother poison her father, brother and sister.

Rachel was arrested the day after Diane. 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 had agreed to testify against her mother if she went to trial, was sentenced in March to two life terms. She is eligible for parole after 42 and a half years.

Both mother and daughter have since filed motions to vacate their pleas. Their lawyers declined comment to PEOPLE, citing the pending motions.

The arrests, confession, pleas and sentencing all started with the pastor. What compelled him to call police, investigators say, was the final stroke of the family’s never-ending bad luck:

When Diane, who spent countless hours at the church as its longtime organist, failed to tell her pastor that her daughter was in the hospital fighting for her life.

“She was at church and someone else told him that Sarah was at the hospital and wasn’t expected to survive,” McAmis says. “He was so troubled and bothered, and that’s why he had to come forward.”