A man from Minnesota is facing murder charges after being accused of using a prohibited toxic substance to poison his roommate, leading to the roommate’s death.

Authorities detained Stuart Hanmer, 35, on Wednesday following an inquiry into the demise of Cody Ernst, 33, who passed away on June 22. According to a criminal complaint cited by local media St. Cloud Live, Hanmer and Ernst shared a room at a recovery facility; Ernst had been living there for several months before Hanmer joined him in May.

After Hanmer’s arrival, Ernst reportedly started experiencing unusual, painful symptoms that necessitated multiple hospital visits over the subsequent weeks, according to police reports.

By the date of Ernst’s death on June 22, his condition had severely worsened, leaving him paralyzed and necessitating life support, as mentioned by his former fiancée, Cat Williams, to the local news outlet Inforum.com. She described his death as an exceptionally cruel and horrific tragedy.

When Ernst was admitted to the University of Minnesota Medical Center on June 20, the St. Cloud Police reported that doctors found “an extremely high and lethal level of the heavy metal thallium in his body,” according to local news St. Cloud Live.

Thallium was used as a rodent poison and insecticide until its use was banned in the United States decades ago. Minnesota Public Radio reported that it is still used in electronics manufacturing.

According to the criminal complaint, Hanmer was allegedly very curious about it.

The criminal complaint stated that after investigators started looking into Hanmer following Ernst’s death, they allegedly found several Google searches for information about thallium. Those search terms allegedly included: “How long does it take if thallium poisons you,” “How much thallium nitrate is fatal,” “Is thallium the most toxic,” and “Is thallium metal in elemental form toxic.”

Hanmer also reportedly searched how to purchase thallium, which investigators confirmed he did — Hanmer allegedly spent $162.56 in three online transactions on 25 grams of thallium metal. The criminal complaint said Hanmer signed for a package at the sober living facility on May 14, two days before Ernst went to the hospital for the first time after experiencing an “episode of vomiting and seizure-like activity.”

The searches and the purchases were conducted in April, the criminal complaint stated. Hanmer allegedly searched more about thallium in May. Police also said that Hanmer watched a YouTube video on his phone in April and again in May about how to create thallium sulfate.

When investigators spoke to Hanmer on July 7, after Ernst’s death, he reportedly told police he and Ernst would “smoke marijuana and drink coffee together.” He claimed to investigators that he had never heard of thallium poisoning until Ernst died.

Hanmer was arrested on Wednesday following an investigation that involved local law enforcement and the Federal Bureau of Investigation. He was charged with second-degree intentional murder and booked into the Stearns County Jail, where he is being held on $4 million with no conditions, or $2 million with conditions. His next court date is scheduled for Sept. 19.