Police believe that Ina Thea Kenoyer, 47, may have had financial motives for the killing of 51-year-old Steven Edward Riley Jr, and court documents state she thought she would inherit $30m when he died.
A criminal complaint in the case states that the suspect believed Riley would leave her after he received an inheritance.
Mr Riley was initially brought to Trinity Hospital but was transferred to a Bismarck hospital where he later died. Autopsy results determined that the cause of death was poisoning.
A search of the couple’s home found a bottle containing anti-freeze, as well as a beer bottle and plastic mug which also contained the substance, reported KFGO.
Officers from the Minot Police Department arrested Kenoyer on Monday 30 October and charged her with Class AA Felony Murder. She is being held at the Ward County Jail.
In North Dakota, a class AA felony could carry a maximum penalty of life in prison without the possibility of parole if there is a conviction.
“This case was extremely complex,” Investigations Commander Capt. Dale Plessas said.
“Thank you to everyone who provided us with information that helped our investigators piece this together.”
The force added that the investigation remains ongoing.