On November 1, 2017, police in Lombard, Illinois, stopped 32-year-old Dwan Thompson after an officer clocked him driving 52 miles per hour, 17 miles over the speed limit.
During the stop, an officer saw part of a marijuana cigarette in Thompson’s car. The officer would later testify that Thompson appeared intoxicated. A Breathalyzer test came back negative for alcohol, and at the police station officers asked Thompson to provide a urine sample for analysis. He was charged with speeding, DUI, drug possession, and using marijuana within two hours of operating a motor vehicle.
Thompson entered a not-guilty plea in DuPage County Circuit Court. He would later tell the website Injustice Watch that he had been at a concert that evening but hadn’t smoked marijuana in more than two hours.
THC doesn’t actually show up in urine. What does appear are metabolites, the byproducts of THC as the chemical is processed through the bloodstream, the liver, and then the kidneys.
While police commonly use a Breathalyzer to measure a motorist’s blood-alcohol content, no such test exists for marijuana. As a result, forensic examiners must either test a motorist’s blood, urine, or saliva.
Jennifer Bash, a former toxicologist with the Illinois State Police, analyzed Thompson’s urine. She ran a department at the Analytical Forensic Testing Laboratory (AFTL) at the University of Illinois Chicago (UIC), that analyzed urine samples for law enforcement officers in DuPage County and other counties in northeast Illinois.
Additional information tied to this forensic misconduct can be found here, in our Groups Registry.
Kevin McMahon, an assistant public defender in DuPage County, represented Thompson. According to Injustice Watch, McMahon questioned Bash several times prior to Thompson’s trial about her report on Thompson’s urine. He told the reporter that Bash’s report didn’t say whether Thompson was over the legal limit, and his confusion over her findings led him to hire a toxicology expert when the case went to a bench trial in October 2018 before Judge Anthony Coco.
Bash testified that as THC is metabolized in the liver, a molecule called glucuronide attaches to it, and this “conjugated compound” is then excreted in urine. She said her testing used hydrolysis to remove the glucuronide, allowing the THC to be pulled out of the urine into an organic solvent. Another part of the sample, she testified, does not undergo hydrolysis, and reveals the presence of THC that never was attached to glucuronide. She referred to this as “free THC.” Bash testified that free and conjugated THC both contain delta-9 THC and adding or removing glucuronide does not change the chemical properties of delta-9 THC.
THC has several isomers, which are compounds with the same formula but different atomic arrangements. The delta-9 isomer is the principal psychoactive agent in marijuana. Delta-8, although also psychoactive, is not illegal in Illinois and other states when derived from hemp, as opposed to marijuana.
Bash testified that she found conjugated THC in Thompson’s urine sample at a concentration of 27.3 nanograms per milliliter, plus or minus 3.3 nanograms. That did not include any free THC. She said the only way the THC could have showed up in Thompson’s urine was through consumption.
Since 2016, the state’s legal limit has been 5 nanograms of tetrahydrocannabinol (THC) per milliliter of blood or 10 nanograms per milliliter of other bodily fluids. A nanogram is one billionth of a gram.
John Wetstein, the toxicology training coordinator for the Illinois State Police Division of Forensic Sciences, testified for the defense.
He said conjugated THC in a person’s urine had no direct contact with the central nervous system and no pharmacological effect; it didn’t get people high or impact their motor skills.
Asked whether delta-9 THC was present in Thompson’s urine, Wetstein said, “When you say delta-9 to me I am interpreting that to mean ‘free THC’ and no, not present.”
But later in his testimony, Wetstein said the level of THC in Thompson’s urine was 27.3 nanograms per milliliter of delta-9 “after they have just been broken apart from [the] glucuronide.”
On October 12, 2018, Coco convicted Thompson of driving under the influence and sentenced him to court supervision.
Thompson appealed, arguing that conjugated THC and free THC were not the same thing; only the presence of the second could sustain his conviction.
The Illinois Appellate Court, Second District, affirmed his conviction on June 14, 2021. The court said that Illinois law did not distinguish between free and conjugated THC. Bash had testified that the conjugation of the THC did not form a new molecule. Wetstein had testified that the process formed a new compound, but also said the testing “reveal[ed] what was there to begin with.”
The court said it didn’t matter whether the THC in Thompson’s urine affected his central nervous system; that relationship wasn’t part of the statute.
In January 2022, the Journal of Analytical Toxicology published an article that detailed problems with distinguishing between the delta-9 and delta-8 isomers. The report said this could create a situation where a person was incorrectly charged with using an illegal drug.
Bash’s supervisor read the article, according to Injustice Watch , and asked her whether that had been an issue at their lab. The lab would eventually acknowledge a problem internally, while telling outsiders that their equipment could distinguish between the isomers.
In 2023, the DuPage Public Defender’s Office had 10 clients facing DUI-cannabis charges, nine from the village of Carol Stream. Bash’s test results were at the heart of these cases, and McMahon brought in Marilyn Huestis at a pre-trial hearing in an effort to bar Bash from testifying at any trials. Huestis was a former director of the chemistry and drug metabolism section at the National Institute on Drug Abuse and an expert on THC’s impact on driving.
Huestis testified that free THC didn’t show up in the urine. She said its metabolites could remain in urine for up to 24 days after a person consumed marijuana, which underscored the problems with using urine testing. She said toxicologists didn’t consider free THC and its metabolites to be the same thing.
Prosecutors dismissed the 10 cases that brought Huestis to Illinois.
After Huestis’s testimony, the UIC lab suspended testing urine for THC. The lab closed for human testing in 2024.
On January 31, 2025, Bob Berlin, the state’s attorney for DuPage County, dismissed Dwan’s conviction and 17 other cases involving what he said was incorrect detection and quantification of THC levels by the UIC lab.
“The successful prosecution of the cases dismissed today relied upon accurate analysis of submitted samples and reliable results,” Berlin said. “With the validity of the test results called into question, I could not, legally, ethically and in good conscience, continue the prosecution of these select cases.”
– Ken Otterbourg
Posting Date: 02-12-2026
