tl;dr: In the U.S., can a "not guilty by reason of insanity" (a.k.a., NGRI or NGROI) defense be offered after a guilty verdict but before sentencing?
In criminal prosecutions in the U.S. it is common and generally considered prudent for a defendant to refuse to expose himself to questioning at trial. This forces the prosecution to use independent evidence to prove beyond a reasonable doubt that the elements of the crime charged were satisfied.
A defendant may want to entertain a claim that he was insane at the time a crime was committed, but avoid entering that claim when there is a significant probability that the state will fail to obtain an conviction on the merits of the case against him.
So my question is: If a jury returns a guilty verdict for a crime, can a defendant subsequently (but before sentencing) argue to the court that he was insane? Or does that defense always have to be offered at trial for the crime, before the case is sent to the jury?