Jury nullification is the term for when a jury declines to convict a defendant despite overwhelming evidence of guilt. This can be a form of civil disobedience, a political statement against a specific law, or a show of empathy and support to the defendant.
“It’s not a legal defense sanctioned under the law,” said Cheryl Bader, associate professor of law at Fordham School of Law. “It’s a reaction by the jury to a legal result that they feel would be so unjust or morally wrong that they refuse to impose it, despite what the law says.”
One reason it exists is because there’s no way to force jurors to rule a certain way. Once jurors go into deliberation, what happens in that room stays in that room.
Taken to its logical conclusion, there’s nothing stopping a jury from voting unanimously either way. They could vote to convict a person they think is innocent (which happens, especially when used against minorities and especially during Jim Crow). They could vote “not guilty” for a person they think is guilty.