Washington — The Justice Department on Wednesday ordered federal prosecutors to stop pursuing criminal charges and drop all pending cases targeting the sale of illicit “defeat devices” that are used to tamper with air pollution control systems in diesel-powered vehicles, according to a memo seen by CBS News.
The edict, issued by Deputy Attorney General Todd Blanche, marks the first time that the Justice Department has formally taken steps to scale back environmental criminal enforcement since President Trump took office in January 2025.
Although the Trump administration took drastic steps throughout 2025 to roll back environmental rules targeting greenhouse gas emissions, many of those actions focused on regulations or civil enforcement, as opposed to criminal environmental enforcement.
In justifying the decision, Blanche cited a new and untested legal theory that runs counter to conclusions reached by both career federal prosecutors and attorneys for the Environmental Protection Agency, according to internal government records reviewed by CBS and three sources familiar with the matter.
The theory posits that the violations could not be prosecuted as crimes under the Clean Air Act, and could only be pursued as civil offenses.
A Justice Department spokesperson could not be immediately reached for comment.
Blanche’s memo comes several months after Mr. Trump in November pardoned Troy Lake, a Wyoming-based diesel mechanic who served seven months in federal prison for conspiring to violate the Clean Air Act by disabling emissions-control devices inside diesel trucks.
The pardon came at the urging of Wyoming Republican Sen. Cynthia Lummis, who alleged that the Lake case represented an example of a “weaponized” prosecution by the Biden administration. She did not cite any evidence for her claim.
Lummis has also championed legislation that would strip the Environmental Protection Agency’s ability to regulate air pollution rules for vehicle emissions and ban the federal government from forcing auto manufacturers to install emissions control systems.
Blanche’s order could potentially impact more than a dozen pending criminal cases across the country targeting companies and individuals who allegedly sold after-market emissions defeat devices, as well as more than 20 ongoing investigations, according to two sources familiar with the matter and court filings.
Several of the pending criminal cases, including two in different districts in Pennsylvania, were indicted in 2025 during the first year of Mr. Trump’s second term in office, court filings show.
The Clean Air Act requires the EPA to regulate air pollution levels generated by vehicles.
In order to comply with those rules, auto manufacturers are required to install emissions control systems to reduce the level of pollutants, such as including nitrogen oxides and carbon monoxide.
It is unlawful to tamper with those systems, but there’s a robust black market for after-market emissions defeat devices because deleting or tuning them can help boost horsepower and improve mileage.
Historically, the EPA and the Justice Department have focused on defeat devices used in diesel vehicles because of the greater pollutant levels they cause.
A 2020 study by the EPA found that in the last decade, emissions controls had been removed from some 550,000 diesel pickup trucks, leading to the emission of 570,000 tons of excess oxides of nitrogen.
The Justice Department’s most high-profile Clean Air Act criminal case related to emissions cheating was Volkswagen.
In 2017, at the tail end of the Obama administration, the company pleaded guilty to criminal charges that it sought to deceive the EPA and state regulators in California by installing defeat devices into its emissions control systems in a failed attempt to cheat emissions tests.
As part of the plea, Volkswagen paid a $2.8 billion criminal fine, and also agreed to pay another $1.5 billion in separate civil resolutions.
After Mr. Trump was inaugurated for his first term, the EPA decided to start scrutinizing after-market emissions defeat devices and went on to make it an investigative priority.
Untested defense bar arguments
The push to kill all of the pending defeat device cases was championed by Adam Gustafson, the principal deputy assistant attorney general for the Justice Department’s Environment and Natural Resources Division who previously worked for Boeing and at the EPA, according to two of those sources and government records seen by CBS News.
He has not specialized in the practice of criminal environmental law.
Although Gustafson has previously signed off on at least some of the pending indictments involving after-market defeat devices, a new and novel defense bar argument that surfaced over the summer later changed his mind, the sources said.
In July, an autobody shop owner named Tracy Coiteux appealed her criminal conviction under the Clean Air Act for tampering with emissions control systems before the U.S. Court of Appeals for the 9th Circuit.
Her attorneys put forth a legal theory alleging that she cannot be held criminally liable because the software associated with emission controls, known as “onboard diagnostic systems,” is not “required to be maintained” under the Clean Air Act.
For this reason, they claimed that such an offense can only be charged as a civil violation, not a criminal one.
Since July, defendants in at least one other pending prosecution have tried to use it to get the case dismissed.
An internal EPA memo reviewed by CBS News shows that career attorneys disagree with the arguments made by defense lawyers in the 9th Circuit case. The memo argues that there are “multiple respects” in which diesel truck emissions software systems are “required to be maintained” under the law, and therefore tampering with them can be a crime.
“When Congress enacted the Clean Air Act, legislators sought to ensure that regulated motor vehicles/engines would meet applicable emission standards not only at the time of manufacture and initial sale, but thereafter in everyday use,” the memo says.
Although the 9th Circuit has not yet ruled on the matter, the legal theory resonated with Gustafson, who started raising questions about the pending cases, one of the sources said.
After Lake was pardoned in November, the topic picked up steam and Gustafson began reaching out to prosecutors with pending cases and asked them to justify the criminal charges, two of the sources said.
Because some of the pending cases are being handled by other U.S. attorney’s offices and not by the office that Gustafson leads, he could not order all of the cases to be dismissed on his own.
He sought support from Blanche’s office, and also from the EPA’s incoming head of the Office of Enforcement and Compliance Assurance, Jeffrey Hall, whom the Senate confirmed on Dec. 18, three sources said.
Shortly before Blanche issued his memo, Hall told staff that he had “carefully examined EPA enforcement for tampering with onboard diagnostic units” and that after speaking with the Justice Department, he was directing EPA to “no longer investigate or pursue criminal cases” related to the tampering of emissions control software.