On Monday, the nation’s attention was focused on the Rocky Mountain college town after a gunman reportedly killed at least ten people, including a police officer, at a local supermarket. CNN reported that one law enforcement official said the weapon used was an AR-15-style rifle.

That kind of weapon was at the center of a landmark legal battle between the gun lobby and the city of Boulder after municipal officials in 2018 “passed two ordinances banning the possession of assault weapons and large-capacity magazines in the wake of the mass shooting” at a school in Parkland, Florida, according to the Denver Post. Colorado has been the site of some of the most high-profile mass shootings in American history, including shootings at Columbine High School, Planned Parenthood of Colorado Springs, the Aurora Theater, and the STEM school in Highlands Ranch.

A federal lawsuit backed by the local chapter of the NRA aimed to invalidate Boulder’s local ordinance, and all other potential assault weapon bans in Colorado. At the time, right-wing activist John Caldara, who filed the lawsuit, insisted that “what Boulder is doing now is putting gun owners back into a closet. And that goes against everything Boulder claims to stand for.”