It doesn't go to zero, however!
If you're measuring the intelligence of criminals who have been caught, why would you expect it to be otherwise?
IOW, you're recording the intelligence of a specific subset of criminals - those dumb enough to be caught!
If you expand your samples to all criminals you'd probably get a different number.
Inversely correlated with crime that's caught and successfully prosecuted, you mean, because that's what makes up the stats on crime. I think people too often forget that we consider most criminals "dumb" because those who are caught are mostly dumb. Smart "criminals" either don't get caught or have made their unethical actions legal.
To the best of my knowledge, none of the individuals believed to have an IQ >200 have committed an actual crime.
The closest I found is William James Sidis's arrest for participating in a socialist march.