A woman who worked as a nurse in a Missouri jail is accused of using antifreeze to fatally poison her husband so she could marry a convicted killer with whom she had developed a romantic relationship, police said.

Amy Prater Murray, 40, of Iberia, is charged with first-degree murder, second-degree arson, armed criminal action and tampering with physical evidence in a felony prosecution, according to Missouri court records. She is being held in the Miller County Jail in lieu of $750,000 bond.

Miller County Sheriff's Office officials said the case began with a 911 call Dec. 11 reporting a fire at 9 Janice Drive in Iberia, the home where Josh and Amy Murray lived. Once firefighters had the blaze extinguished, 37-year-old Josh Murray was found dead inside.

Investigators with the Missouri State Fire Marshal's Office determined the fire had been set in the couple's bedroom using an accelerant, according to Sheriff's Office officials.

An autopsy showed Josh Murray died of antifreeze poisoning, officials said. It also showed he was already dead when the fire broke out, according to ABC17 in Columbia.

Court documents obtained by the news station allege Amy Murray started the fire after her husband was dead. She then took the couple's 11-year-old son and their dogs to a McDonald's about 22 miles away in Osage Beach.

Murray is alleged to have told detectives she came home from the outing to find the house on fire, but the smoke was too thick to go inside and find her husband.

According to Inside Edition, however, investigators found a McDonald's sandwich on a counter inside the house.

Eugene August Claypool Jr.

Credit: Missouri Department of Corrections

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Credit: Missouri Department of Corrections

The documents indicate Amy Murray worked as a nurse at the Jefferson County Jail in Hillsboro, where she encountered inmate Eugene Claypool. According to Missouri Department of Corrections records, Claypool, 39, is serving a life sentence for second-degree murder.

Amy Murray was recorded telling Claypool during a phone conversation that she no longer wanted to be married to Josh Murray, ABC17 reported. She was also recorded after her husband's death telling Claypool they could be married because Josh Murray was now "out of the picture."

She also mentioned getting a lawyer for Claypool to try to get him released from prison early, according to the news station. Inside Edition reported that Claypool, who has already served 18 years in prison, becomes eligible for parole after 25 years behind bars.

Claypool was 21 years old when he went to prison for the Christmas Day 2000 stabbing death of Donald Hardwick, a 72-year-old disabled man who had made headlines of his own two years earlier when he won a $1.7 million Missouri Lottery jackpot.

Claypool and a co-defendant, Jeffrey Williamson, broke into Hardwick's home in search of cash they believed he kept there. Both later pleaded guilty to the murder, Inside Edition reported.