A Missouri woman used poison to kill her husband -- so she could marry a man doing life behind bars for murder, investigators alleged.

Police said Amy Murray, 40, of Iberia, poisoned her husband with antifreeze, placed his body on a bed and set him on fire, Fox 5 Atlanta reported. After starting the fire last December, Murray then went to a McDonald’s with her 11-year-old son and dogs, Fox 22 Columbia reported, citing a probable cause statement.

The court documents showed that at the time, Murray was having an affair with a prisoner at the Jefferson City Correctional Center where she worked as a nurse, Fox 22 reported.

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According to the documents, in recorded phone conversations Murray told the inmate, Eugene Claypool, 40, she didn’t want to be married to her husband anymore and she could marry Claypool because her husband was dead and “out of the picture,” Fox 22 reported.

Clayton has been locked up for more than 18 years in the deadly stabbing of a 72-year-old Missouri man who won $1.7 million in a lottery game. He was arrested in December 2000.

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The pair also talked about getting an attorney to spring Claypool from prison early, the Jefferson City News Tribune reported.

Murray has been charged with first-degree murder and armed criminal action in the death of her husband, Joshua Murray.

She was jailed in lieu of $750,000 bond.

Iberia is about two hours southwest of St. Louis.