A woman has been arrested after allegedly poisoning her boyfriend to death over “financial motives,” police said.

Steven Edward Riley Jr. -- a 51-year-old man from Minot, North Dakota -- died suddenly early last month on Sept. 5 at a hospital in the state capital of Bismarck, according to a statement from the Minot Police Department released on Monday.

Following an autopsy, authorities determined that Riley’s cause of death was poisoning and his surviving girlfriend, 47-year-old Ina Thea Kenoyer was arrested on Monday and charged with the killing of her boyfriend through poisoning, police said.

“Police believe that Riley’s girlfriend, 47-year-old, Ina Thea Kenoyer, Minot, had financial motives to murder Riley,” said the Minot Police Department. “Kenoyer is charged with Class AA Felony Murder and is being held at the Ward County Jail.”

While authorities said there were “financial motives” for Kenoyer to poison her boyfriend, police did not release any further information on the case or what may have led them to that conclusion.

“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 investigation into the case is currently ongoing.