After the United States Supreme Court decision in Atkins (2002), the ABA Guidelines were amended as follows:

"the constitution forbids the execution of persons with mental retardation, making this a necessary area of inquiry in every case." Commentary to ABA Guideline 4.1, p. 44 

We must always conduct a comprehensive Atkins investigation in a manner consistent with best practices articulated by the American Association on Intellectual and Developmental Disabilities (AAIDD) -- even if the client graduated from high school, attended college, likes to read books, can play chess, is described as "smart" by witnesses, or seems "normal" when we talk to them.  

Intellectual disability is  never excluded as a possibility in a capital case -- it is an issue to "rule in", not to rule out.