MADISON, Wis. — A state appeals court reinstated a lawsuit Thursday against a website that facilitated the purchase of a gun used in a mass shooting in suburban Milwaukee five years ago, rejecting arguments that federal law absolves the website's operators of liability.

A restraining order barred Radcliffe Haughton from possessing a firearm, but he purchased a gun through firearms trading site Armslist.com and used it to kill his wife and two of her co-workers at Azana Salon & Spa in Brookfield in 2012. He wounded four other people during the shooting before killing himself.

The court ruling sends a signal nationwide that websites that enable gun deals must take reasonable care to prevent sales to people prohibited from purchasing firearms, said Jonathan Lowy, an attorney with the Brady Center to Prevent Gun Violence, which filed the lawsuit.

"This is an extremely important win," Lowy said. "This is very persuasive precedent to courts around the country."

Armslist attorney Joshua Maggard didn't immediately reply to an email seeking comment.

Zina Daniel Haughton had taken out a restraining order against her husband that prohibited him from possessing a firearm. But he bought a gun and ammunition anyway from a person he met through Armslist.com, according to court documents. Gun buyers and sellers can use the site to find and contact each other.

The Brady Center to Prevent Gun Violence brought a lawsuit in 2015 on behalf of Zina Daniel Haughton's daughter, Yasmeen Daniel, alleging the website's operator, Armslist LLC, is liable for the incident.

Daniel argued in the lawsuit that the site allowed prospective buyers to limit searches for sellers to private sellers who don't have to conduct background checks and the site prevented users from flagging content as illegal.

She also maintained that users weren't required to register their account with the website and the site was designed to enable buyers to evade waiting periods by enabling deals with private sellers.

Milwaukee County Judge Glenn Yamahiro dismissed the complaint, finding that federal law states website operators aren't liable for publishing information provided by someone else and Daniel failed to allege that Armslist created or develop illegal content on its page.

The 1st District Court of Appeals reversed Yamahiro. The appellate court found that Daniel's lawsuit doesn't treat Armslist as the publisher of information provided by someone else but instead seeks to hold the company liable for its own conduct in designing and running the website in ways that caused injury.

"(The law) does not protect a website operator from liability that arises from its own conduct in facilitating user activity, as is the case here," the court said.