DENVER (NewsNation) — A Colorado dentist accused of killing his wife by slipping poison into her drinks was formally charged Thursday with first-degree murder.

James Craig, 45, was arrested on suspicion of first-degree murder last week, shortly after his wife died after being taken off life support during her third trip to a hospital this month.

As Angela Craig languished in the hospital, with doctors unable to figure out what was wrong with her, police in the Denver suburb of Aurora allege her husband was meeting with a fellow dentist who flew in for visits with him. Police began investigating Craig after his dental practice partner and friend, Ryan Redfearn, told a nurse that Craig had ordered potassium cyanide even though they did not need it for their work, according to an arrest warrant laying out evidence gathered by investigators.

After allegedly Googling questions such as, “Is Arsenic Detectable in Autopsy?” investigators believe Craig put arsenic in one of the protein shakes he routinely made for his wife for their workouts March 6 and then, after she survived, ordered a rush shipment of potassium cyanide that he told the supplier was needed for a surgery. Craig had asked an office manager not to open that package but another employee did, leading to its discovery and eventual disclosure to authorities, the document said.

According to court records, he is being represented by the public defender’s office, which does not comment on cases.

Steffan Tubbs sat in Craig’s dentist chair for maybe 30 or 40 hours in recent years as a patient.

“I’m still in shock,” Tubbs told NewsNation’s Chris Cuomo last week.

Tubbs said Craig was known as a “family man” who he never suspected could have committed such a crime.

“I was absolutely stunned when I opened up the story and I saw a mugshot: ‘There’s my dentist!’” Tubbs added. “This is just something that I couldn’t believe.”

The Associated Press and NewsNation writer Tyler Wornell contributed to this report.