Mother convicted of poisoning her family maintains her innocence

Despite confessing to police that she poisoned her husband, son and daughter with antifreeze, Diane Staudte says she is innocent.

“I said what I was told to say -- I’m saying there’s more to that than what people know,” Staudte said in an exclusive interview with “20/20.” Despite her claims of innocence, there is no evidence that anyone but Diane Staudte and her daughter, Rachel, were behind these shocking crimes.

Nearly six years after pleading guilty to two counts of first-degree murder, Diane Staudte said she’s ready to share the chain of events that led to her life imprisonment without parole.

In 2012, Staudte seemed to be living a normal life in Springfield, Missouri. She was trained as a nurse, was an active member of her church and the breadwinner for her family of six. Her husband Mark Staudte was a local musician who looked after their children.

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Staudte described her children as “little professors they all had their little special interests, but boy they knew everything about their special interests.”

On Easter Sunday in 2012, 61-year-old Mark Staudte died of what appeared to be natural causes which some attributed to an unhealthy lifestyle. His bandmates noted that he had been acting strangely on Friday night, saying that he was slurring his words and his skin appeared yellow. It was noted that there was a ring of blood around his mouth at the time of his death, according to police reports.

Jeff Sippy, who was then the pastor at Redeemer Lutheran Church, the family's church, said he immediately felt like something was wrong.

“There was nothing in me that believed that it was of a natural cause,” Sippy said in his first time speaking publicly about the Staudte case. “I didn’t believe that he died of a stroke. A heart attack. Or in his sleep. I just didn’t. There’s nothing scientific. There’s nothing professional about my observation. But my first words were ‘no way.’ He did not just die.”

Five months after Mark Staudte’s death, tragedy struck again when the Staudte’s son, Shaun Staudte, was found dead after having flu-like symptoms. A ring of blood was also found around his mouth, but his autopsy ruled that his death was due to prior medical issues, including a seizure disorder, according to his autopsy report.

Then in June of 2013, alarm bells started going off for the police, according to Detective Neal McAmis.

Diane Staudte's eldest daughter, Sarah Staudte, was taken to the hospital by her mother and her sister Rachel Staudte.

Sarah Staudte was admitted to the ICU with a brain bleed and organ failure. While in the hospital, doctors began to suspect poisoning was the cause.

Simultaneously, samples were recovered from Shaun Staudte’s autopsy, where testing revealed the presence of ethylene glycol, one of the raw components of antifreeze.

Sippy said after Sarah Staudte was hospitalized, he called in a tip to the Springfield Police Department.

“I said that I believed that Shaun Staudte’s death did not appear to me to be of natural causes. And that this would benefit from investigation,” said Sippy.

Ethylene glycol is not a typical part of normal toxicology screenings and requires specific testing to detect, which is why it was missed during the initial autopsy.

McAmis brought Diane and Rachel Staudte in for questioning.

In interrogation tapes obtained exclusively by ABC News, Diane Staudte admitted to using antifreeze to poison her family members by putting it into her children's Coca-Cola and husband's Gatorade.

During the interrogation, McAmis asked why she did not bring her husband to the hospital.

“I hated his guts– I guess I'd just had enough,” Staudte told detectives.

In 2022, her most recent interview, she continued to claim that her husband had trouble with hard drugs and alcohol, but that she was not the one to poison him.

“Mark was with some people that are very dangerous -- people have disappeared -- I was told in jail that Mark had been green-lighted,” Staudte said, referring to a possible hit placed on her husband. “I’m saying somebody probably came in and gave him something.”

Before 2022, Diane Staudte had never told the police nor her lawyers that her husband had been associated with “dangerous people” or that her husband had been involved with hard drugs. According to authorities, there is no evidence to support these claims.

During her questioning with McAmis, she was asked why she decided to poison her son, who was autistic.

"Shaun would be interfering with whatever I would do," Staudte told McAmis in 2013. "He was more than a bother... more than a pest."

Staudte’s middle daughter, Rachel Staudte, was also brought in for questioning. At the time, she denied any involvement in the poisoning of her family members.

A police search of the family’s home recovered Rachel Staudte’s journal that revealed she knew what was going on and was helping her mother to research and plan how to poison her family members.

When presented with the journal as evidence, Rachel Staudte confessed to helping her mother.

Rachel and Diane Staudte were arrested and charged for the deaths of Mark and Shaun Staudte. Both pleaded guilty to the murders and the assault of Sarah Staudte.

Rachel Staudte pleaded guilty to second-degree murder in 2015 as part of a plea deal in exchange for testifying against her mother. She received two life terms with the possibility of parole after 42-and-a-half years.

Diane Staudte entered an Alford plea which acknowledges that prosecutors had enough to convict her without admitting guilt. In 2018, she was sentenced to life imprisonment without parole.

Sarah Staudte has made a miraculous recovery from the ICU but has sustained permanent damage with lifelong effects. She is currently in assisted living.

When speaking about Sarah Staudte, Diane Staudte said “I’m sorry for what she went through but you know I’m sorry for what everybody goes through,” said Staudte. “I’m sorry for what I’ve had to go through.”

Diane Staudte said she was sorry for what her family had been through but despite confessing to police, now denies having any part in the poisoning. At one point, she alluded to being poisoned herself, which there is no evidence of. McAmis affirms, “There is nothing whatsoever to show that anybody was involved in this case other than those mentioned already. Diane and Rachel... the ones that killed their family.”