CR is likely not unintelligent, but he is unsophisticated and uneducated. To answer you I'm going to go back to a posit I made before about a cultural milieu basis for invalidating CR's Miranda. CR might have been incapable of believing that he has a right to not incriminate himself. In his home country, when the police bring you in for a crime this serious, you cooperate with them and tell them what they want to know or the consequences could be dire. He showed LE the body because he truly believed that he had to, or else. While he has been in the US for 8 years, he lived, working long hours, in a sub-cultural ghetto. Even with exposure to the outside world, MSM is constantly headlining stories of LE shooting and killing minorities (further enforcing his beliefs about LE's brutality and Lethality), as was common practice in his country in the first third of the last century in Mexico. In this country, these occurances are the exception, in his country it is rule. While CR did not fear MT, he is deathly afraid of the Federalies who actually did pick him up. The FBI have an imposing presence all their own, and I am certain that DCI is not far behind them.
What we saw in his court appearance was cultural shock. He is in way over his head, and has the fear felt by any caged animal that can't get out and is no longer in control of its destiny or environment.