The widow of a Chicago police commander has sued an online gun marketplace for enabling the sale of a firearm allegedly used in his 2018 shooting death, according to reports.

The 9-millimeter Glock pistol that four-time felon Shomari Legghette is accused of using to kill Cmdr. Paul Bauer was sold to him via private sale by a Wisconsin man on Armslist.com, according to a lawsuit obtained by the Chicago Sun-Times.

The lawsuit — filed Wednesday in federal court in Wisconsin by Bauer’s wife, Erin, and the nonprofit gun control group Brady Legal — claims the website intentionally exploited gaps in America’s gun laws by facilitating illegal gun sales and purchases without background checks.

That negligence, according to the filing, allowed Legghette, 46, to obtain the alleged murder weapon in Bauer’s February 2018 on-duty slaying. Legghette, who was barred from owning a firearm due to his prior felony convictions, is expected to stand trial for first-degree murder in Bauer’s death later this year, the Chicago Tribune reports.

Bauer, a married father who was a 31-year department vet, was the highest-ranking Chicago cop killed on the job in decades, according to the newspaper.

Jonathan Lowy, lead counsel for Brady Legal, formerly known as the Brady Campaign to Prevent Gun Violence, said Legghette obtained the Glock because of the “thriving, anything-goes” internet gun marketplace.

“Commander Bauer’s family brings this suit because they want guns to be sold legally and responsibly, and they do not want another family to suffer as they have,” Lowy said in a statement. “Irresponsible gun sellers and online marketplaces should clean up their act, or expect to be held accountable. We look forward to proving our case in court.”

Legghette allegedly shot Bauer six times during a confrontation in Chicago on Feb. 13, 2018. The officer was pronounced dead at a hospital.

The lawsuit seeks unspecified monetary damages and injunctions to force Armslist to prevent sales to people prohibited from owning guns.

If successful, the litigation would be the first time an online seller is held liable for a slaying involving a weapon sold on its platform, according to the Sun-Times.

A message seeking comment from Armslist was not immediately returned Thursday.