Mark and Shaun Staudte Murders: How Did They Die? Who Killed Them?

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It seemed like the Staudte family kept getting hit by one tragic event after another over 14 months, starting in April 2012. After the family patriarch, Mark, passed away, the son, Shaun, died a few months later. It wasn’t until another family member was admitted to a hospital under grave circumstances that the authorities began to suspect something fishy. ABC News’ ‘20/20: Home Sweet Murder’ looks at what led to Mark and Shaun’s death and the identity of their killers that made for a shocking revelation. So, let’s find out what happened then, shall we?

How Did Mark and Shaun Staudte Die?

Mark Alan Staudte met Diane while studying at St. John’s College in Winfield, Kansas. They married in December 1985, eventually having four children: Shaun, Sarah, Rachel, and Briana. Around the time of his death, the family lived together in Springfield, Missouri. While Diane worked as a nurse, Mark played guitar with a local blues band, sometimes supplementing income by working odd jobs like tending bar. Shaun, who was diagnosed with autism at a young age, required care at home.

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On April 8, 2012, Mark suddenly died at home in what was thought to be of natural causes. The 61-year-old wasn’t known for a healthy lifestyle, and despite a bloody ring around his mouth, the death wasn’t investigated further. About five months later, in September 2012, 27-year-old Shaun died as well. Like his father, Shaun also had a ring of blood around his mouth, but given his history of seizures, the cause of death was cited as “prior medical issues.” Both bodies were cremated soon after the deaths.

Who Killed Mark and Shaun Staudte?

While the family was still reeling from the loss of Mark and Shaun, the oldest daughter came down with flu-like symptoms in June 2013. Sarah, then 24, was rushed to the hospital, where the doctors quickly realized some of her organs were failing. Around the same time, the family’s pastor called the authorities claiming Diane could be involved with the deaths. There was suspicion regarding how Mark and Shaun died and Sarah fell sick.

The nurse at the hospital claimed that Diane didn’t seem too worried about Sarah’s health condition and said she made jokes and talked about a vacation to Florida. The pastor also said Diane seemed unemotional after Mark and Shaun’s deaths. Soon, the authorities decided to take a closer look at those deaths and brought in Diane for questioning. Initially, she denied hurting her children, but her story began to change when pressed further.

Initially, Diane claimed that her husband and son drank antifreeze to kill themselves. When the police didn’t find that story believable, she admitted mixing antifreeze in Mark’s energy drinks and Shaun’s sodas. In another chilling confession, Diane stated she poisoned Sarah “over four days.” Regarding Mark, she said, “By then, I hated his guts. He would throw things at me. He would throw things at the kids. I guess I’d just had enough.”

Diane said that Shaun became a burden on her, and she resolved to get rid of him, calling her son “more than a pest.” Finally, Sarah lived at home because she had trouble finding a job after graduation. The mounting college debt was something Diane did not want to pay for, and she decided to kill her. While the mother initially said she was solely responsible, it came to the fore that Rachel was also involved.

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At the time, Rachel was Diane’s favorite daughter. A search of the house led to Rachel’s diary, which mentioned Mark and Shaun’s deaths long before they happened. So, during questioning, Rachel admitted to helping with planning and researching the crimes. According to Rachel, Diane was the mastermind who initially brought up Mark’s death. However, Diane then talked about killing Shaun and Sarah the same way, and Rachel reluctantly went along with it.

In the end, Rachel took a deal and agreed to testify against Diane. She was convicted for her part and sentenced to life in prison. As for Diane, she pled guilty to one count each of first-degree murder, second-degree murder, and first-degree assault in January 2016. Then 53, she was sentenced to life in prison without the possibility of parole. During her interrogation, Diane said, “I’m not a perpetual killer. I’m just stupid. I regret doing it. I really do. I’ve screwed up everybody. I’ve screwed up my whole family.”

Read More: Where is Rachel Staudte Now?