I recently met with a client who had a jury trial for a Domestic Battery charge. After several days of a trial and deliberations, the jury could not agree on a verdict and the judge declared a mistrial. Shortly after the mistrial was declared, the prosecution decided that they would retry the client and he came to my office looking to hire me for the second trial. The client had several questions about what happens at a re-trial and weather Double Jeopardy applied to his case. I answered his questions and realized that people misunderstand what Double Jeopardy means.
In order for you to be convicted of a crime by a jury, all 12 members of the jury must agree that you are guilty. At the same time, in order to be found not guilty of a crime by a jury, all 12 members of the jury must agree that you are not guilty. Their verdict must be unanimous. If a jury is unable to come up with a unanimous verdict, the Court will declare a mistrial. A mistrial does not necessarily mean that the case is over. When a mistrial happens, the prosecution will decide whether they want to try you once again for the same crime. The decision about whether the state will try you again for the same crime is a decision that rests with the prosecution. From experience, prosecutors will take a variety of factors into consideration when deciding whether to have another trial. A major factor for prosecutors is how close did they come to winning the first jury trial? In other words, if a vast majority of the jurors were in favor of finding you guilty, it is much more likely that the state will try you again. If the vast majority of the jurors were in favor of finding you not guilty, it is much more likely that the state will drop the case and not seek another trial.
The legal grounds for you not to be subjected to another trial can be found in the Fifth Amendment to the United States Constitution and Section 10 of the Illinois Constitution.