The more I think about the absurdity of their actions and the gauntness both CT and KR display in their mug shots the more I think their abusing of meth or cocaine begins to make more sense.
Once you move from casual to daily use of these two drugs your thought processes and decision making erodes extraordinarily quickily. When someone has been up for 3-5 days on an extended binge the mind begins to work against itself. You start to "think" you have really great ideas and are thinking very quickly and making well thoughtout decisions because the drugs are helping you focus on the problem at hand when the reality is completely opposite.
Then when something bad happens instead of doing what a logical person would- clear the mind to make better decisions -the drug addict thinks he needs more drugs to help sort through the problem efficiently. Hence the spiral.
You have to have at some point interacted with these types of people to have some understanding of how skewed their realities become.
That being said-cops spot these folks easily due to their actions, mannerisims, and physical quirks. If CT and KR really were abusing drugs hard enough to account for the really stupid choices they made you would think it would be in the initial notes when they were questioned by the locals.
I have a hard time believeing Craig bungled things this badly without being "affected" in some way.