It's not unusual for a jury to vote not guilty when the evidence isn't strong enough to make a compelling case against the defendant. However, sometimes even when the defendant is obviously guilty, juries will still return a not-guilty verdict and let the person walk free. Here's how this may come about, why it's legal, and the chances of it happening in your criminal case.
About Jury Nullification
The phenomenon of a jury issuing a not-guilty verdict when all evidence points to the defendant's guilt is called jury nullification. When this occurs, juries typically acknowledge the defendant is guilty based on the law, but they justify the verdict by stating the law is immoral or being unjustly applied to the defendant.
For instance, jury nullification occurred frequently during the 1850s when northern juries would refuse to convict people of harboring slaves, even though it was against the law (the Fugitive Slave Act) to help or hide escaping slaves. According to some estimates, up to 4 percent of trials litigated today result in nullification.
Jury nullification is a holdover from when America was a British Colony. The power of juries to render contrary decisions in cases regardless of the evidence is sustained by a combination of the responsibility the court places on the jury to render verdicts, the Fifth Amendment prohibiting double jeopardy, the inability of attorneys to force jurors to produce a particular verdict, and the lack of punishment for juries who do produce verdicts contrary to the evidence.
Unlike with a hung jury, jury nullification ends the case against the defendant. The person cannot be prosecuted further in that court for that crime, and the prosecutor cannot appeal the jury's decision. As you can imagine, getting a jury to take your side and set you free despite the evidence can be immensely beneficial. However, the odds of this occurring are very low for several reasons.
First, most people don't know jury nullification is an option. People who serve on juries assume they must render a verdict based on the evidence and the applicable laws. This is because, in modern times, judges are reluctant to advise jurors of their right to nullify the charges, because they are concerned this may result in a rash of unreasonable and illogical nullifications as jurors vote along their sympathies, something that famously happened in the Emmett Till trial where an all-white jury voted to acquit the men who killed Emmett Till despite knowing those men were guilty.
Not only do judges avoid telling juries about nullification, they also typically prohibit prosecutors and defense attorneys from speaking about this option during their opening or closing remarks. Juries can only work with what they know, and they can't nullify your case if they don't know that's an option.
Second, jury nullification requires the jury to feel sympathy for you or think the law is unfair or being unjustly applied in your situation. This can be very difficult to accomplish, especially if you're charged with crime that goes against the public's moral sensibilities.
For instance, a New Hampshire jury nullified a felony charge in a case where a man was charged with cultivating marijuana, which he claimed he was doing it as part of his religion (he was Rastafarian). This surprising turn of events could be attributed to a culture shift where medicinal and recreational marijuana use has gained acceptance. On the other hand, someone who was charged with a DUI may not find a lot of sympathy with the jury since driving while intoxicated is still heavily censured.
Attempting jury nullification would require quite a bit of legal maneuvering. If you're convicted of a crime, you should discuss this and other legal options for avoiding a conviction with a criminal law attorney.