DENVER (TNND) — A Colorado dentist accused of killing his wife by poisoning her protein shakes will face the start of his murder trial on Tuesday.

James Craig, 47, allegedly used cyanide and tetrahydrozoline, a substance found in over-the-counter eye drops, to kill his wife, 43-year-old Angela Craig.

Craig pleaded not guilty to several charges, including first-degree murder.

The Aurora Police Department said his wife passed away after her third visit to the hospital within a month, as she said she was experiencing severe headaches and dizziness.

A warrant for Craig's arrest was issued after his wife was declared medically brain dead and "doctors made the decision to take the victim off life support," according to authorities.

Prosecutors previously said he had searched online for answers to questions such as, “Is arsenic detectable in an autopsy?” and “How to make murder look like a heart attack."

Additionally, after his arrest in 2023, he allegedly offered a fellow jail inmate $20,000 to kill the case’s lead investigator and offered someone else $20,000 to find people to falsely testify that Angela Craig planned to die by suicide, according to prosecutors.

Craig's attorneys have questioned the reliability of the inmate's claims, said the police were biased against the dentist and that tests of the protein shake containers didn't reveal signs of poison.

It was also reported that he appeared to be having an affair with a fellow dentist, though a motive has not yet been determined.

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Editor's note: The Associated Press contributed to this article.