The United States v. Fields case ended up on a federal death sentence imposed on Fields for commitig a federal capital offense.
This sentence was made largely on the basis of the opinion of a psychiatrist who stated that he could predict Fields would be a risk to society in the future.
The problem here is that the psychiatrist issued this crucial testimony without doing any testing or offering any objective empirical data whatsoever.
To this day, there's still much debate involving how a Court can determine risk to society or future violence from an individual, in a safe and reliable manner that reaches necessary standards for a case of such magnitude assessing death penalty.
Hope this helps!