The day the "too dumb" defense works is the day we can open all the cell doors and close down the prisons, because that's everyone's defense.
> Delinquents and criminals average IQ scores 8 to 10 points lower than noncriminals, which is about one-half a standard deviation. IQ and criminal behavior are negatively correlated at about r = -. 20 (Hirschi and Hindelang; Wilson and Herrnstein).
We call this “financialization”.
That doesn't help with estimating levels of non-detected crimes of course.
There's no way he can plead stupidity.