Prosecutors in DuPage County, Illinois, dismissed 18 convictions for driving under the influence of marijuana in 2025 after learning of problems with the reports generated by the forensic laboratory that performed drug tests on the defendants.
Illinois legalized marijuana in 2019, and the law took effect on January 1, 2020. It is still illegal to drive under the influence of marijuana.
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.
THC has several isomers, which are compounds with the same formula but different atomic arrangements. In Illinois, the testing is done for the delta-9 isomer, 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.
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.
At crime laboratories run by the Illinois State Police, officials decided that only blood tests would give reliable results, according to extensive reporting on the issue in Injustice Watch . But the Analytical Forensic Testing Laboratory (AFTL) at the University of Illinois Chicago (UIC), originally created in 2004 to test for illicit drugs in racehorses, opted to test urine samples.
The university hired Jennifer Bash, a former forensic toxicologist with the Illinois State Police, to set up this section of the AFTL laboratory, and she began analyzing urine samples provided by law-enforcement officers in DuPage County and other counties in northeast Illinois.
On November 1, 2017, police in the village of Lombard 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 officers asked Thompson at the police station to provide a urine sample for analysis. He was charged with speeding, DUI, possession, and using marijuana within two hours of operating a motor vehicle.
Thompson entered a not-guilty plea. He would later tell Injustice Watch that he had been at a concert that evening but hadn’t smoked marijuana in more than two hours.
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 website that Bash’s report didn’t say whether Thompson was over the legal limit, and his confusion over her findings led him to hire his own toxicology expert when the case went to a bench trial in 2018 before Judge Anthony Coco in DuPage County Circuit Court.
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.
At trial, 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.
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.
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.”
In his testimony, Wetstein said that the reading of 27.3 nanograms per milliliter were of delta-9 THC “after they have just been broken apart from [the] glucuronide.”
Wetstein was asked whether delta-9-tetrahydrocannabinol was present in defendant’s urine when it was sent to the laboratory. Wetstein responded, “When you say delta-9 to me I am interpreting that to mean free THC and no, not present.” Wetstein testified that removal of the glucuronide during the testing process did not cause a new chemical structure to form. Rather, “[i]t reveals what was there to begin with.” Wetstein explained, “You are not making anything new. You are reverting it to its perhaps former self.” However, the “binding process” creates a different compound. Wetstein acknowledged that the 27.3 nanograms per milliliter were of delta9-tetrahydrocannabinol “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 Division, 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 use of an illegal drug.
Bash’s supervisor read the article, according to Injustice Watch, and asked Bash 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 persuade the court 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 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.
Heustis would later tell Injustice Watch: “What [Bash] did was wrong. Forensic science is all about truth. Everything we do—the DNA people, the gun casing people, all the forensic sciences—is about using scientific evidence to get at the truth. And if something is wrong scientifically, and then it’s used in a manner in which it affects the truth, then that could affect anyone.”
After Huestis’s testimony, the UIC lab suspended testing urine for THC.
In early 2024, AFTL shut down human testing at its lab and told Bash it wouldn’t be renewing her contract. An audit by an accrediting agency found substantial problems at the lab, including a lack of equipment maintenance and insufficient checks and balances on the work of analysts.
In the spring of 2024, Albert Larsen, the lab’s director, wrote to state’s attorneys in 17 counties about the issues related to distinguishing between the two THC isomers. “This issue has been of concern since we first learned of its existence,” he wrote.
On January 31, 2025, Bob Berlin, the state’s attorney for DuPage County, dismissed 18 cases involving what he said was incorrect detection and quantification of THC levels by the UIC lab.
One of the cases was a felony; the rest, misdemeanors. The convictions occurred between 2018 and 2023. Other than Thompson, all the defendants had entered guilty pleas.
None of the defendants had received active sentences for their convictions.
“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,” Berlin said.
In November 2024, UIC hired the Taft Stettinius & Hollister law firm to conduct an independent review to address allegations that the lab had concealed its flawed methodologies, provided inaccurate results, and failed to disclose its deficiencies. It also investigated whether lab employees had provided false testimony.
Taft’s report, released May 28, 2025, said that the lab had used proper methodologies in testing for the presence of delta-9 in urine samples. But the allegations that the lab used flawed methodologies related to distinguishing between delta-8 and delta-9 were “founded as to the methodologies used by AFTL after AFTL became aware or should have been aware of the commercial availability of hemp-derived Delta-8 products because Delta-8 then became a potentially relevant factor and AFTL’s methodologies did not test for the presence of Delta-8 in test samples.
The report said there was no evidence that the lab’s employees knew their testing was flawed, that they had provided inaccurate results to police and prosecutors, or that they had knowingly provided false testimony. The report said that Bash, through her attorney, declined to be interviewed.
The report said the lab’s decision to stop testing human samples was a business decision. “[It] was the culmination of a process, which began in 2022, that weighed the financial burden of AFTL’s human testing along with the decision to suspend the forensic science programs at the College,” the report said. “The allegations that AFTL closed human testing due to issues related to flawed methodologies are unfounded.”
– Ken Otterbourg
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Posting Date: 10-20-2025
Last updated: 10-20-2025