Former Milwaukee police officers Graham Kunisch right, and Bryan Norberg left, who were shot and seriously wounded by a gun illegally purchased at Badger Guns. Photograph: Rick Wood/AP

Jurors have ordered a Wisconsin gun store to pay nearly $6m to two Milwaukee police officers who were shot and seriously wounded by a gun purchased at the store.

The ruling came in a negligence lawsuit filed against the store, Badger Guns, by the two officers. The lawsuit alleges the shop allowed an illegal sale despite several warning signs that the gun was being sold to a “straw buyer”, or someone who was buying the gun for someone who couldn’t legally do so. Jurors sided with the officers, ruling that the store was negligent in selling the gun.

Defense attorneys declined to comment after Tuesday’s verdict. An attorney for the officers said he expected years of appeals.

Officer Bryan Norberg and retired Officer Graham Kunisch were both shot after they stopped Julius Burton for riding his bike on the sidewalk in the summer of 2009. Surveillance video shows the officers scuffled with Burton and pushed him against a wall before he shot them both in the face.

Investigators said Burton got the weapon a month before the confrontation, after giving $40 to Jacob Collins to make the purchase from Badger Guns in West Milwaukee.

One bullet shattered eight of Norberg’s teeth, blew through his cheek and lodged into his shoulder. He remains on the force but argues that his wounds have made his work difficult. Kunisch was shot several times, resulting in him losing an eye and part of the frontal lobe of his brain. He said the wounds forced him to retire.

Jurors ordered the store to pay Norberg $1.5m and Kunisch $3.6m, in addition to $730,000 in punitive damages.

The gun shop’s defense lawyers denied wrongdoing and said the owner, Adam Allan, couldn’t be held financially responsible for crimes connected to a weapon sold at his shop. Badger Guns, previously known as Badger Outdoors, has since closed and been replaced by a gun shop called Brew City Shooters Supply. All three entities have been run by Allan family members.

Authorities have said more than 500 firearms recovered from crime scenes had been traced back to Badger Guns and Badger Outdoors, making it the “number one crime gun dealer in America”, according to a 2005 charging document from an unrelated federal case. A former federal agent has also said the shop had failed take necessary precautions to prevent straw purchases.

Norberg and Kunisch cited those details in their lawsuit, saying they showed a history of negligence.

The issue gained attention in the US presidential campaign when Democratic front-runner Hillary Rodham Clinton recently said she would push for a repeal of the George Bush-era gun law that Badger Guns’ lawyers said shielded the store from liability claims.

Burton pleaded guilty to two counts of first-degree attempted intentional homicide and is serving an 80-year sentence. The man who purchased the gun, Jacob Collins, got a two-year sentence after pleading guilty to making a straw purchase for an underage buyer.