Ina Thea Kenoyer thought she was her boyfriend's "common law" wife and that she was entitled to part of his inheritance, per the police.
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A North Dakota woman was charged with murder on Monday and accused of poisoning her boyfriend with antifreeze after learning he may have stood to inherit $30 million.
Ina Thea Kenoyer, 47, is accused of killing Steven Edward Riley, 51, who died on September 5 at a hospital in Bismarck, North Dakota, according to the Minot City Police Department.
An autopsy showed that the cause of death was poisoning, police said, adding that officials believe Kenoyer "had financial motives to murder Riley."
Kenoyer is being held at the Ward County Jail in Minot, the police statement added.
Riley was found unresponsive on September 4, the day before he died, after emergency services were called to the couple's home, The New York Times reported, citing an affidavit filed by a Minot PD officer.
He was taken to an emergency room and then transferred to the hospital in Bismarck, where he later died, per The Times.
The coroner found that he'd died of poisoning from ethylene glycol, which is found in antifreeze, The Times reported.
Investigators said Kenoyer had grown upset that Riley was set to receive an inheritance of around $30 million but wanted to leave her, according to the outlet.
He had traveled to an airport with Kenoyer and several friends to meet a lawyer and discuss his inheritance on September 3, per the outlet. Riley fell sick on this trip and said he felt drunk, per The Times.
But when his friend suggested he seek medical help, Kenoyer "was adamant" that he was suffering from heat stroke and just needed to return home and rest, the affidavit said, according to the outlet.
Kenoyer told officers that Riley had been drinking heavily and suffered from heat stroke, but a toxicology report determined that Riley had no alcohol in his system when he died, according to The Times.
Officials searching the couple's home also found a Windex window cleaner bottle, a Coors Light beer bottle, and a plastic mug that were suspected to contain antifreeze, per the outlet.
Detectives said Kenoyer acknowledged that she had served sweet tea to Riley on the day he fell ill, with the affidavit noting that sweet drinks can be effective at disguising antifreeze, according to The Times.
Kenoyer only called for medical help after Riley was ill for about 12 hours at home, and later told detectives that some of his inheritance was hers because she was his "common law" wife, per The Times, citing the affidavit.
She explained to investigators that she had been dating Riley for a decade, per CBS News, which also obtained the affidavit.
However, when detectives told Kenoyer that such common law marriages are not recognized in North Dakota, she became "incensed," the affidavit said, per CBS.
Kenoyer has been charged with a class AA felony murder, the most severe murder charge in the state, and faces life in prison.
