A medical examiner determined Betty Bowman died after being poisoned by a drug that a tipster told police her husband had researched.

A grand jury in Minnesota has indicted a doctor accused of fatally poisoning his wife, and upgraded charges against him to first-degree murder, authorities said.

Dr. Connor Bowman, 30, was arrested in October and charged with second-degree murder linked to the death of his wife, Betty Bowman. She was 32 years old when she died Aug. 20, only four days after she was admitted to a hospital.

Investigators collected evidence that indicated Connor Bowman, who once worked for poison control, “may have given Betty Bowman a drug for an ailment she did not have,” Rochester police had said.