The Fourth Amendment to the United States Constitution prohibits “unreasonable searches and seizures”. An arrest, including a DUI arrest, constitutes a seizure.
If a court (judge) finds that a seizure is unreasonable, the arrest is deemed illegal. For the most part, any evidence gathered as a result of the arrest is also illegal.
Due to United States Supreme Court decisions, the remedy for an illegal arrest is to suppress (“throw out”) the evidence. Without evidence, the state cannot prove its case, resulting in dismissal of the charges. (This is what is meant by “a technicality”).
The Constitution does not specify when a seizure is or is not “unreasonable”, a wise choice since what can be viewed as unreasonable in one time and place can be considered reasonable in another. It is left to the courts to decide where to draw the line.
The Illinois court system has three layers. The first is the trial court. This is what most people consider “court” with judges, juries, and presentation of witnesses and other evidence all playing a part.
The next level, if is either side is unhappy with the decision and has the time and money to take it further, is the appellate court. In Illinois, there are five appellate court districts, broken down by geography. So, for instance, the Fourth Appellate District, whose physical location is in Springfield, would hear an appeal from a Macon County (Decatur) case.
Appellate court cases do not involve either party presenting additional evidence. Instead, the lawyers argue the case based upon the evidence presented at the trial court.
Each of the five appellate courts consists of a three-judge panel that, after hearing the arguments and reading the briefs (papers) of the lawyers, issues a written decision usually published for all to read. All trial court judges are required to follow the rules set out in the published appellate court decisions.
The highest level of appeal in the Illinois system is the Illinois Supreme Court. Appeals to the appellate court are automatic, whereas the Supreme Court for the most part has the final say over what appeals it will hear.
The Court accepts only a small percentage of the cases it is asked to hear. Thus, when someone proclaims they will “take the case all the way to the Supreme Court”, they are probably engaging in wishful thinking.
If either the state or the accused believes that the state supreme court has misread the Fourth Amendment requirements, that party may seek an appeal with the United States Supreme Court but that court hears even fewer appeals than the state supreme court. So in reality, most search and seizure law in Illinois is decided in the five appellate districts.
In matters involving the Fourth Amendment, all state courts, including state supreme courts, are required to provide criminal defendants with at least as much search and seizure protection as the United States Supreme Court says the Constitution requires. A state court may decide to give the accused additional rights but that is rare. Most, including Illinois, follow in “lockstep” with the United States Supreme Court.