A Colorado dentist accused of killing his wife by lacing her protein shakes with poison is set to enter a plea in court to a first-degree murder charge on Tuesday.

Police said James Craig, who began an affair before his wife’s March 18 death, 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.” In the following days, Craig’s wife, Angela Craig, then Googled symptoms she was having including vertigo, shaking and cold lips, said District Attorney John Kellner at a July preliminary hearing.