Police have arrested a Hyrum man accused of trying to poison his mother-in-law by putting rat poison in her soy milk.

The woman discovered the poison when flakes from the blue-colored pellets fell out as she poured the milk on her cereal Sunday morning, said Cache County sheriff's Lt. Matt Bilodeau. She poured out the rest of the liquid and found two to three tablespoons of the poison pellets in the bottom of the container, he said.

She called police and reported that she suspected her 36-year-old son-in-law.

"There's been some issues in the past with him ... strange events," Bilodeau said. Officers arrested him Monday on suspicion of surreptitious administration, or secretly slipping someone a controlled substance. Formal charges have not yet been filed, according to the Cache County Attorney's Office.

The D-Con brand poison dissolves slowly and had not fully mixed with the milk, Bilodeau said. It had been there no more than 24 hours. The poison acts as a blood thinner. Bilodeau did not know whether the amount could have killed her.

"We don't know the motive. I think the intent is clear," Bilodeau said.

The man and his wife lived with the mother-in-law for several years before moving out to live in their own home with their two children, he said. Though they are capable of taking care of themselves, both the man and his wife are considered "low functioning" adults, Bilodeau said. He has few social skills and cannot work in most jobs, he said.

He previously pleaded guilty to burglary and kidnapping charges in connection with a 1991 home invasion robbery, according to Utah court records.