The online firearms marketplace Armslist cannot be held liable for a pair of shootings in Wisconsin that involved guns bought through ads posted on the site, a federal appeals court has ruled.

On Monday, a three-judge panel for the Seventh Circuit Court of Appeals affirmed the lower court’s dismissal of the two suits in a joint decision. The court found that even though the circumstances surrounding the cases “are grave and the allegations are serious,” Armslist cannot be found liable for negligence under Wisconsin law because it is not a firearms dealer.

“Concluding that the allegations in this first category can proceed would impose the responsibilities of firearms dealers on actors which the Wisconsin legislature has not chosen to regulate in this manner,” Judge Michael Brennan, a Donald Trump appointee, wrote on behalf of the court. “It would also hold Armslist LLC liable for failing to operate as an arm of the state where Wisconsin has not given it this function. Just so, on allegations about background checks and transaction records—the second category—the Wisconsin legislature has not chosen to regulate websites or private sellers…or to oblige them with enforcement.”

The ruling deals a blow gun-control activists’ push to apply civil liability to gun companies for crimes committed with firearms by third parties—a legal maneuver that is generally precluded by the federal Protection of Lawful Commerce in Arms Act. Though gun-control advocates have long used this strategy, it has experienced a revival in recent years thanks to the high-profile backing of the policy by President Joe Biden and the recent $73 million settlement between Remington’s insurers and the families of Sandy Hook victims. The movement has also succeeded in passing new legislation in blue states designed to make it easier for crime victims to sue gun businesses.

Armslist has been a particularly frequent target, though most attempts to sue the company for its business practices have been similarly unsuccessful. That’s because, unlike most firearms-related businesses, the site does not actually make or sell any guns. Instead, it operates as a digital classified ad platform, akin to Craigslist, where private sellers can post listings offering to sell their firearms to one another. As such, it is not “engaged in the business of importing, manufacturing or dealing in firearms and having a license as an importer, manufacturer or dealer issued by the federal government,” and cannot be held to the same liability standards as “firearms dealers” under Wisconsin law.

The plaintiffs who sued Armslist included the father of Sara Schmidt, who was murdered by her estranged husband in 2018, and the widow of Chicago Police Commander Paul Bauer, who was murdered by a multiple-time convicted felon in Chicago the same year. Both perpetrators in each homicide were prohibited possessors but were able to obtain handguns through private sales conducted in Wisconsin that were advertised on Armslist’s website.

The families argued that the site is negligent because it does not implement certain operational safeguards, such as requiring sellers to identify themselves, perform background checks, or require waiting periods for the delivery of sold firearms. They also claimed that the company actively “aided and abetted” illegal weapons sales by not implementing stricter sales policies; they allege site operators were aware that firearms listed for sale on the site end up on the criminal black market.

They argued the site’s disclosures that it does not get involved in transactions between parties and does not certify their legality was evidence of that fact. However, the judges were unpersuaded by those arguments.

“Bauer also fails to point to a specific action Armslist LLC took in ‘continuing’ to design and administer the website to promote illegal sales that might indicate an intent to assist; rather, Bauer seems to contend that armslist.com aided and abetted illegal transactions simply by virtue of its continued existence,” Judge Brennan wrote. “But the failure to prevent unlawful conduct is alone insufficient to state a claim for aiding and abetting.”

“These provisions no more endorse illegal activity than a ‘swim at your own risk’ sign placed at a hotel pool endorses using the pool to drown another,” he added.