What Evidence Does the Prosecutor Use in Colorado DUI Cases?
Ever wondered how the state builds a case against you in a DUI charge? It might seem like it all comes down to the blood alcohol content (BAC) number. But in reality, prosecutors in Colorado rely on a wide range of evidence—starting from the moment an officer first notices your vehicle.
Let’s break it down.
What Evidence is used in DUI Cases?
View Transcript
The evidence a prosecutor uses in DUI cases is based on the totality of circumstances, starting with the initial traffic stop. The officer must have had reasonable suspicion that a traffic or criminal violation occurred. This usually involves driving-related behaviors, such as weaving, failing to stop at a stop sign, or making a wide turn—enough to justify stopping the vehicle.
From there, the case depends on what the officer observes after making contact with the driver. They look for signs such as slurred speech, bloodshot or watery eyes, odor of alcohol, and whether the person can divide their attention—for example, by talking while retrieving a driver’s license, registration, and insurance. These observations form what’s known as indicia of impairment.
Additional indicators may include unsteadiness when stepping out of the vehicle, difficulty answering questions, or confused or nonsensical responses. Once the officer suspects impairment, they may request the person perform Standardized Field Sobriety Tests (SFSTs)—also known as roadside tests. These tests are voluntary, although officers are often persuasive in getting people to agree to them.
The three most common SFSTs are:
– Horizontal Gaze Nystagmus (HGN) Test – The officer holds an object in front of the driver’s eyes and looks for involuntary eye movements or lack of smooth tracking.
– Walk-and-Turn Test – Walking heel-to-toe in a straight line while following instructions.
– One-Leg Stand Test – Balancing on one foot while counting aloud.
These tests are used to gather evidence of impairment and help the officer decide whether there’s probable cause for arrest.
If the officer decides to arrest the individual, Colorado’s Express Consent law takes effect. This law means that by driving in Colorado, you’ve already consented to a chemical test of your blood or breath to determine alcohol or drug levels. While you can refuse the test, refusal has consequences.
Chemical tests are usually performed at a hospital or police station. The blood or breath test results play a major role in trial. A result of 0.08% BAC or higher is a significant factor for the prosecution.
Officers may also offer a Preliminary Breath Test (PBT) at the roadside. This test is not admissible in court, but it helps establish probable cause for arrest. If the PBT shows a BAC over 0.08%, it further justifies taking the person into custody.
If a driver refuses chemical testing, officers can sometimes obtain a warrant to compel the test. In some cases, they allow the refusal, but this decision has implications. On one hand, there’s no test result proving intoxication, which can help the defense. On the other hand, the refusal itself can be used against the defendant at trial, raising the question: “Why refuse if you weren’t impaired?”
Additionally, refusal often results in longer license suspension periods through the DMV, further complicating the legal consequences.
It All Starts with the Traffic Stop
Every DUI case begins with the traffic stop. Under Colorado law, an officer needs reasonable suspicion to pull you over. That could be:
- Drifting between lanes
- Running a stop sign
- Taking a turn too wide
- Or simply driving in a way that raises concern
Even minor infractions can justify a stop. If you’re curious about what counts, our page on Colorado DUI laws has more.
Once pulled over, everything you say and do can potentially become evidence.
Observations That Become “Indicia of Impairment”
Next comes the officer’s first interaction with you. This is often the biggest piece of evidence in a DUI case. Colorado officers are trained to watch for signs of impairment, known in police reports as “indicia of impairment.” This includes:
- Slurred speech or trouble forming sentences
- Bloodshot, glassy, or watery eyes
- An odor of alcohol on your breath
- Fumbling for your license or registration
They are even taking note of your mannerisms as you try to hold a conversation while searching for your wallet. If you pause awkwardly or struggle to multi-task, that gets noted.
Small things can become large points at trial. Prosecutors will often argue these observations show your mental or physical faculties were impaired “to the slightest degree” (the legal threshold under Colorado’s DWAI (Driving While Ability Impaired) statute.
Field Sobriety Tests: Building the Officer’s Case
If the officer suspects you’re impaired, they might ask you to perform Standardized Field Sobriety Tests (SFSTs).
These tests are voluntary in Colorado, despite how forcefully some officers suggest them. The three most common are:
- Horizontal Gaze Nystagmus (HGN): The “follow my pen” test, looking for jerky eye movements.
- Walk-and-Turn: Nine heel-to-toe steps, a pivot, then nine back.
- One-Leg Stand: Stand on one foot and count aloud.
The officer will watch for swaying, raising arms for balance, and losing count. Anything that might indicate impairment.
It’s worth noting: these tests aren’t perfect. Many sober people struggle with them, especially in bad weather or if they have injuries. That’s something our Colorado DUI defense attorneys often highlight in court.
Preliminary Breath Tests vs. Chemical Tests
At the roadside, an officer may use a Preliminary Breath Test (PBT). This is a small handheld device that gives a quick BAC estimate.
Important: The PBT is not admissible at trial in Colorado. It’s only used to help establish probable cause for arrest.
If you’re arrested, Colorado’s Express Consent Law kicks in. The Express Consent law states that by your driving on Colorado roads, you’ve already agreed to submit to a chemical test (either breath or blood) if an officer has probable cause to believe you’re impaired.
This test is far more critical because:
- A BAC of 0.08% or higher creates a “permissible inference” that you were under the influence.
- The prosecution will lean heavily on this number.
Refusing the chemical test doesn’t necessarily help. It leads to automatic license suspension for at least one year, and prosecutors can tell the jury about your refusal, suggesting you had something to hide.
Additional Evidence: Video, Warrant Blood Draws, & More
Today, many police cars are equipped with dash cams, and officers often wear body cameras. This means:
- Your driving behavior may be captured before the stop.
- Your interactions, field sobriety tests, and even the arrest may all be on video.
If you refuse a chemical test, officers can also seek a warrant for a forced blood draw, which then becomes powerful evidence.
Putting It Together: The “Totality of Circumstances”
Ultimately, a DUI case in Colorado is rarely about one single piece of evidence. Prosecutors build a case using the totality of the circumstances. They’ll try to stack:
- The reason for the stop
- The officer’s observations
- Field sobriety test results
- PBT readings (for probable cause only)
- Official chemical test results
- Video or audio recordings
- Statements you made (admissions, confusion, or conflicting stories)
Why This Matters for Your Defense
Because so many small details get bundled together, having an experienced DUI attorney is critical. A strong defense might challenge:
- The validity of the stop (was there really reasonable suspicion?)
- How the field sobriety tests were administered
- Whether the breath machine was calibrated
- Chain of custody on a blood sample
Understanding the Colorado DUI cost implications is also crucial for your defense strategy. If you’re facing DUI charges in Colorado, don’t leave your future to chance. Our team at Right Law Group has handled thousands of DUI cases, many of them resulting in reduced charges or outright dismissals. You can learn more on our Colorado DUI penalties page.
For those facing a first DUI offense, remember that even first-time charges can escalate to felony DUI under certain circumstances. Additionally, any sentence includes requirements like community service as part of the penalty structure.
Final Thoughts
The next time someone says “it’s all about the BAC,” you’ll know better. Prosecutors use every piece of evidence they can gather. That’s why it’s crucial to know your rights, understand what’s at stake, and have a legal team that knows how to pick apart the prosecution’s case piece by piece.
Need help? Call us today or reach out for a free case evaluation.
Author Bio
Alexis Austin Litle is the CEO and Managing Partner of Right Law Group, a criminal defense law firm she founded in 2018, with convenient locations in Colorado Springs, Castle Rock and Highlands Ranch. With almost a decade of experience in criminal defense, she has zealously represented clients in a wide range of legal matters, including DUIs, misdemeanors, felonies, domestic violence, and other criminal charges.
Alexis received her Juris Doctor from the University of Denver — Sturm College of Law and is a member of the Colorado Bar Association. She has received numerous accolades for her work, including being named among the “Top 40 Under 40” in 2018 by The National Trial Lawyers and featured in Authority Magazine’s “Top Lawyers” series.