Types of Evidence Prosecutors Rely On In Illinois DUI Cases

DUI Arrests in Chicago: What You Need to Know from the Start

In Chicago and throughout Illinois, driving under the influence (DUI) is one of the most aggressively prosecuted misdemeanor and felony offenses on the books. Prosecutors in Cook County and surrounding counties such as DuPage, Lake, and Will take DUI enforcement seriously due to the potential danger impaired drivers pose on public roadways. Whether you’re arrested on Lower Wacker Drive, pulled over near Lake Shore Drive, or stopped on I-55 in the suburbs, a DUI charge can carry devastating legal and personal consequences if not handled properly.

Illinois DUI charges begin under 625 ILCS 5/11-501. It is unlawful to drive or be in actual physical control of a vehicle while under the influence of alcohol, drugs, or any intoxicating compound. A first-time DUI is typically charged as a Class A misdemeanor, punishable by up to 364 days in jail, fines up to $2,500, and a mandatory driver’s license suspension. However, several aggravating factors can escalate a DUI to a felony. These include having a prior conviction, driving without a license or insurance, having a minor in the car, or causing bodily injury. Felony DUIs are categorized as Class 4 to Class 2 felonies, depending on the circumstances, and can carry three to seven years in prison under Illinois law.

Every DUI case in Illinois starts with the same core processes: a traffic stop, a police investigation, and a potential arrest. From there, prosecutors build their cases based heavily on physical, testimonial, and scientific evidence. The strength of that evidence will determine the direction of the case — and whether a defendant may face conviction or walk free.

How Criminal Cases Begin and the DUI Investigation Process in Illinois

Illinois law enforcement officers begin most DUI cases with a traffic stop based on observed behavior or traffic violations. This might be weaving between lanes, failing to use a turn signal, or erratic braking. Under Illinois criminal law, an officer must have reasonable suspicion that a crime or traffic violation has occurred to initiate a stop.

Once stopped, the officer begins building a case by observing the driver’s demeanor. Slurred speech, glassy eyes, an odor of alcohol, and fumbling for documents are commonly cited signs of impairment. If the officer suspects intoxication, the driver will likely be asked to submit to field sobriety tests (FSTs). These include the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg stand — each standardized by the National Highway Traffic Safety Administration (NHTSA).

Police also commonly request a preliminary breath test (PBT) at the scene, although the results are not admissible in court in most circumstances. Instead, they are used to establish probable cause to make a DUI arrest. If arrested, the driver is then taken to a police station, where they are asked to submit to a chemical test — usually a breathalyzer or a blood draw. Refusal to submit to this test will result in an automatic license suspension under Illinois’ statutory summary suspension law, even if you’re never convicted of the DUI.

This is where the legal trouble deepens. From this moment forward, prosecutors begin preparing a case using a variety of evidentiary tools.

The Types of Evidence Prosecutors Rely on in Illinois DUI Cases

The strength of a prosecutor’s DUI case depends on the type and credibility of evidence collected during the investigation. In Illinois, prosecutors generally rely on several categories of evidence to prove DUI charges beyond a reasonable doubt. Each of these has specific rules for admissibility and weight in court.

Police officer testimony plays a central role in any DUI prosecution. Officers testify about their initial observations of the defendant’s driving behavior, interactions during the stop, the defendant’s speech, demeanor, ability to follow instructions, and results of field sobriety tests. Under 625 ILCS 5/11-501.2, the officer’s report and testimony can be used to establish that the driver was under the influence.

Chemical test results are some of the most heavily relied-upon evidence. Breathalyzer tests performed on an approved machine at the station are admissible under Illinois law, provided proper procedures were followed. A BAC (blood alcohol concentration) of 0.08 or higher creates a presumption of impairment. For drivers under age 21, any alcohol in the system is illegal under Illinois’ zero-tolerance law. Blood and urine tests may also be used, especially in suspected drug DUI cases, though they carry different evidentiary requirements.

Video footage from police dash cams or body-worn cameras is also increasingly used in court. This footage can either support the officer’s account or contradict it — which makes reviewing it a critical part of the defense process. Additionally, surveillance footage from local businesses or nearby street cameras may provide context that is favorable or unfavorable to the accused.

Field sobriety tests, though often subjective, are introduced by prosecutors as indicators of impairment. They rely on officer observations and NHTSA standards for how each test is to be administered. But improper instructions, uneven surfaces, medical conditions, and even footwear can affect results — which opens the door for defense challenges.

Finally, eyewitness accounts and expert witness testimony can influence the outcome. Civilian witnesses who observed erratic driving or drinking behavior may be subpoenaed. Medical experts or forensic toxicologists can testify about the accuracy of blood or breath test results.

Penalties, Criminal Records, and Long-Term Consequences in Illinois

Under Illinois DUI laws, penalties vary based on the number of prior offenses and aggravating circumstances. A first-time offense without enhancements is a Class A misdemeanor. Penalties can include jail time (up to one year), a fine up to $2,500, and a driver’s license suspension for six to 12 months.

However, the consequences go far beyond criminal penalties. A DUI conviction creates a permanent criminal record in Illinois, which cannot be expunged or sealed. This means that even a first offense can follow you for life, affecting job opportunities, professional licensing, immigration status, and insurance rates.

Repeat offenders face increasingly harsh penalties. A second DUI conviction results in a mandatory five-year license revocation and up to a year in jail. A third offense becomes a Class 2 felony under 625 ILCS 5/11-501(d), with a minimum 10-year license revocation and potential imprisonment from three to seven years. Causing bodily harm while driving under the influence elevates the charge to aggravated DUI, also a felony.

If convicted, you may be required to install a Breath Alcohol Ignition Interlock Device (BAIID) in your vehicle, attend alcohol education or treatment programs, and face extensive court supervision and probation terms.

The Illinois Criminal Trial Process and DUI Defense Strategies

Once a person is charged with DUI in Illinois, the case proceeds through several phases. First is the arraignment, where the defendant is formally advised of the charges and enters a plea. Then comes pre-trial discovery, during which both sides exchange evidence. Defense attorneys file motions to suppress illegally obtained evidence or to dismiss unsupported charges.

If the case is not resolved through plea negotiations, it proceeds to trial. At trial, the prosecution presents its evidence and witnesses. The defense then has the opportunity to challenge the evidence, cross-examine witnesses, and present alternative theories or defenses.

An example case involved a driver arrested on I-94 in Skokie for DUI. The officer claimed the client failed all field sobriety tests and had bloodshot eyes and slurred speech. However, the dash cam footage showed that the client performed the tests reasonably well, and there was no valid probable cause for the stop — the driver had committed no traffic violations. The defense filed a motion to suppress the arrest, which the judge granted. The entire case was dismissed. This highlights how a seasoned defense attorney can scrutinize every detail and turn a weak prosecution case on its head.

Why You Need a Criminal Defense Attorney in a DUI Case

Every phase of a DUI case presents legal pitfalls that can seriously impact the outcome. From the moment of arrest, police officers are trained to gather evidence that supports conviction. Without an experienced attorney reviewing that evidence, identifying legal violations, and challenging faulty assumptions, a defendant is left exposed.

A DUI attorney evaluates the constitutionality of the stop, the administration of field tests, the procedures followed during chemical testing, and the admissibility of all evidence. A strong legal defense can result in charges being reduced, dismissed, or even an acquittal at trial.

Moreover, attorneys can negotiate alternative sentencing options such as court supervision, which avoids a conviction and keeps your record clean. They also help with license reinstatement procedures and represent clients in administrative hearings with the Illinois Secretary of State.

Common Legal Defenses in Illinois DUI Cases

Several defenses can be raised in an Illinois DUI case, depending on the facts. These include lack of probable cause for the traffic stop, improper administration of field sobriety tests, medical conditions that mimic intoxication symptoms, rising blood alcohol defenses, and challenges to the accuracy or maintenance of breathalyzer devices.

In drug DUI cases, where impairment is alleged based on marijuana or prescription medication, prosecutors must show not only the presence of the substance but that it impaired the driver’s ability to operate the vehicle safely. This is often a point of contention where expert testimony becomes critical.

Choosing the Right DUI Defense Attorney in Illinois

When facing DUI charges, it is essential to hire a lawyer with years of courtroom experience handling similar cases. Look for an attorney with a proven record defending DUI cases, who is familiar with the local prosecutors and judges, and who will personally handle your defense — not hand it off to a junior associate.

At your free consultation, ask direct questions such as: How many DUI cases have you taken to trial? Have you handled cases involving the same chemical tests or circumstances as mine? What are the likely outcomes in my case? What defenses do you think might apply? How will you investigate and fight my charges?

Chicago DUI Defense FAQs Under Illinois Law

Can I be charged with DUI in Illinois if I wasn’t driving but just sitting in my parked car?
Yes. Illinois law allows prosecutors to charge someone with DUI for being in “actual physical control” of a vehicle while intoxicated — even if the vehicle is not moving. Courts consider factors like whether the keys were in the ignition, where the person was sitting, and whether the engine was running.

What happens if I refuse the breathalyzer at the police station?
Under Illinois’ implied consent law, refusing a chemical test after a DUI arrest results in a statutory summary suspension of your driver’s license for one year. This is separate from the criminal DUI charge and goes into effect automatically.

Will a first DUI conviction stay on my record forever in Illinois?
Yes. Illinois does not allow expungement or sealing of DUI convictions, even for first-time offenses. That’s why it is crucial to fight the charge or seek an outcome that avoids conviction.

Can I get court supervision for a DUI?
Court supervision is only available for first-time DUI offenders and only at the discretion of the court. If granted, it allows you to avoid a conviction, but you must complete all conditions set by the judge, such as alcohol education or community service.

How long will my license be suspended after a DUI arrest?
If you fail a chemical test, your license will be suspended for six months. If you refuse testing, it will be suspended for one year. You can challenge the suspension by filing a petition for a hearing within 90 days.

Can a DUI affect my professional license or job in Illinois?
Yes. Many professions — including healthcare, law enforcement, education, and commercial driving — require reporting of DUI arrests or convictions. A DUI can result in license suspension, disciplinary actions, or job termination.

Is DUI a felony or misdemeanor in Illinois?
Most first and second DUI charges are misdemeanors. A third offense or any DUI involving aggravating factors, such as bodily injury or a child passenger, is a felony under Illinois law.

Do I need an attorney if I’m pleading guilty to a DUI in Illinois?
Yes. Even if you plan to plead guilty, a skilled DUI attorney can negotiate better terms, protect your rights, and ensure that you understand all consequences. Unrepresented defendants often face harsher outcomes.

Why You Need a DUI Defense Attorney—and Why You Should Call Us

A DUI conviction is never just a ticket or a slap on the wrist in Illinois. It’s a permanent mark on your criminal record that carries long-term consequences for your license, freedom, job, and reputation. Prosecutors in Cook, DuPage, Will, and Lake Counties aggressively pursue DUI cases with the full force of the law. Without a qualified criminal defense attorney, you risk losing everything.

At The Law Offices of David L. Freidberg, we know exactly how Illinois prosecutors build DUI cases — and how to dismantle them. With decades of experience, we’ve defended countless clients in Chicago and surrounding counties and secured favorable results through dismissal, acquittal, and reduced charges. We handle every case personally and fight to protect your future.

When You Need a Fighter, Call Us

Whether you’re charged in downtown Chicago, Skokie, Maywood, Bridgeview, or Rolling Meadows, we’re ready. We appear regularly in courtrooms throughout Cook, DuPage, Will, and Lake Counties. And we don’t treat aggravated speeding as just another moving violation.

If you were arrested in Chicago, protect your future by contacting The Law Offices of David L. Freidberg. We have decades of experience handling DUI cases in Illinois. Our firm is available 24/7 to provide the legal defense you deserve.

Contact us today at (312) 560-7100 or toll-free at (800) 803-1442 for a free consultation. We’re available 24/7 to serve clients throughout Illinois, Cook County, DuPage County, Will County, and Lake County.