Woman Convicted Of Poisoning Husband, 2 Children Maintains Her Innocence

A woman in Springfield, Missouri, convicted of killing her husband and son and attempting to kill her daughter insisted in a new interview that she is innocent.

Diane Staudte, who was trained as a nurse, is serving a life sentence without parole after pleading guilty to two counts of first-degree murder nearly six years ago in connection to the 2012 deaths of her husband Mark Staudte and their son Shaun Staudte.

Diane admitted to using antifreeze to poison her family members by putting it into her children's Coca-Cola and husband's Gatorade, according to interrogation tapes obtained by ABC News. Diane's daughter, Rachel Staudte, later confessed to helping her mother poison their family.

However, Diane claimed in an exclusive new interview with "20/20" that she "said what [she] was told to say" at the time.

"I'm saying there's more to that than what people know," she insisted.

There is no evidence supporting the claims that anyone but Diane and her daughter Rachel were responsible for the crimes, authorities said.

However, Diane claimed in the interview 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," Diane claimed, suggesting a possible hit was placed on her husband. "I'm saying somebody probably came in and gave him something."

Diane's husband Mark, a local musician, died on Easter Sunday in 2012 of what appeared to be natural causes, which some attributed to an unhealthy lifestyle.

At the time, Mark's bandmates noted that he had been acting strangely and slurring his words, and his skin appeared yellow. There was a ring of blood around his mouth at the time of his death, police reports showed.

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

"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," Sippy told "20/20" of Mark's death.

Five months after his father's death, the couple's son Shaun 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.

Then in June 2013, Diane's eldest daughter, Sarah, was taken to the hospital by her mother and her sister Rachel with a brain bleed and organ failure. Doctors suspected that poison was the cause.

At the time, authorities found the presence of ethylene glycol, one of the raw components of antifreeze, in samples from Shaun's autopsy. Ethylene glycol was missed during the initial autopsy as it is not a typical part of normal toxicology screenings and requires specific testing to detect.

The pastor then made an anonymous call to the Springfield Police Department to report that he believes Mark's and Shaun's deaths and Sarah's hospitalization "needed to be investigated."

Diane and Rachel were brought in for questioning by Detective Neal McAmis, and the mother admitted to using antifreeze to poison her family members.

Diane told authorities at the time she did not bring her husband to the hospital because she "hated his guts" and "had enough."

While she now claims that her husband had been associated with "dangerous people" and had been involved with hard drugs, Diane did not mention these claims to police and her lawyers before her "20/20" interview. There is no evidence to support these claims, authorities said.

During questioning in 2013, Diane also told detectives that she poisoned her son Shaun, who was autistic, because he would "interfere" with whatever she did and was "more than a pest."

Meanwhile, Diane's middle daughter, Rachel, initially denied any involvement in the poisoning of her family members but later confessed to helping her mother after police found her journal. It revealed she knew what was going on and was helping her mother to research and plan how to poison her family members.

Rachel and Diane were arrested and charged for the deaths of Mark and Shaun. Both pleaded guilty to the murders and the assault of Sarah, who survived but sustained permanent damage with lifelong effects and is currently in assisted living.

Diane entered an Alford plea for the two counts of first-degree murder, which acknowledges that prosecutors have enough evidence to convict him without her having to admit to the crime. She was sentenced to life imprisonment without parole in 2018.

Rachel 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.

Despite Diane's claims, McAmis said, "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."