I am not a lawyer, and I will guess gitana will respond, however I thought I may share my understanding of how this would occur.
My understanding is a plea would always be based on the value of what shared testimony can provide the prosecutor. Most often this starts with a proffer agreement, or sometimes called "queen for a day." This is when information is shared under the agreement that anything shared can not be used against the person sharing the information. This also gives the prosecutor the chance, and I would even say obligation, to verify the information provided on proffer.
This is on federal rules, however, I would expect Colorado to follow similar processes.
Criminal Defendant Proffer, Plea & Cooperation Agreements
DA May has thus far shown he is thorough and aggressive. In the first court appearance we heard that they verified some of the information provided such as the stain on the hay and locations of blood in the condo. I would say it is reasonable to think that all parts of KK's proffer were investigated, and that any areas that were in question would have had clarification prior to the plea agreement being drafted and accepted.