Complex sentence: There was some argument that Derrick Lee was perhaps incompetent to stand trial; during psychiatric evaluations he scored an average of 65 on various standardized IQ tests, and a score below 69 is considered to be the threshold for what can be considered mental retardation.
Split into simpler sentences: There was some argument that Derrick Lee was perhaps incompetent to stand trial. A score below 69 is considered to be the threshold for what can be considered mental retardation.