This is not in the constitution but rather than telling you to do some research (which would be quite suited in this case) here is a link to understand jury nullification better.
It says the concept is rooted in British Common Law and has it US roots from just prior to the civil war.
http://en.wikipedia.org/wiki/Jury_nullification
but, like most things, the concept itself results in a combination of a number of other basic concepts (many of which are in the constitution, just like bank fraud may not be there but could still be illegal outside of MA), including the concept of not punishing a jury for it's decision. The topic is most strongly debated currently around how much the precedents or rules around jury nullification should be allowed or required to be stated to people in a jury. Interesting that the link said something like 1/20 juries are said to be nullified. I guess that makes sense because if you are found to be 19/20 guilty, they will still punish you (95% CI used all the time).
I think the concept is that you use jury nullification to get what you want when want you want is different than the clearly stated rules, kind of like civil lawsuits are used when crimes did not occur to still get your way. There are just so many ways to legally break the rules.
Sorry if the link contains too many facts (or things asserted as fact), I know that they can really ruin discussions around here by keeping people from blaming the other party.
Knowing what the constitution says is different than knowing what it means, which we will debate forever and not just on this board. Remember it says:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
Some people see this as saying you have freedom of religion, but it does not say that a state cannot have a religion that a president cannot declare a national religion, etc. Many would argue what I just said. It says literally that congress shall make no law respecting an establishment of religion. Seems to me that recognizing that the catholic church or any church exists at all is clearly unconstitutional. But you may want to argue this too.
Just glad we have an expert here who knows how to do what countless before her including all that wrote it, continue to write it and are paid to interpret it still cannot do... understand it or use it consistently.
LJ do you want clear law that you can use where jury's do not have this right or unclear law where you can nail your banks when they did not break one?