Twenty-six people were killed and 22 wounded when Devin Patrick Kelly opened fire on a church in Sutherland Springs, Texas, in November 2017, in the worst mass shooting in state history.
Kelly, a convicted felon, had a history of domestic violence and mental health problems. He was found dead after the tragedy, after he shot himself.
Families of victims and survivors sued the US government, saying it could have prevented the shooter from legally possessing firearms.
“The court found that the government failed to exercise reasonable caution by reporting Kelly’s antecedents to the FBI and that the government was 60 percent responsible for the harm to the plaintiffs,” the ruling read.
Convicted criminals are generally not allowed to possess firearms, and licensed sellers must check national databases before completing a sale.
Texas gun laws are among the most lax in the country.
Kelly escaped the background check system because the US Air Force, where he served, had not reported two domestic violence convictions five years earlier.
US Air Force spokeswoman Anne Stefanik said the agency plans to appeal the ruling, according to the New York Times.
