Twenty-six people were killed and 22 more wounded when Devin Patrick Kelley opened fire at the First Baptist Church in Sutherland Springs, Texas, in November 2017.

Kelley, a convicted felon, had a history of domestic abuse and mental health problems.

The attack, after which Kelley was found dead having shot himself, was the worst mass shooting in Texas history.

"The Court concluded that the Government failed to exercise reasonable care in its undertaking to submit Kelley's criminal history to the FBI and that the Government was 60 percent responsible for the Plaintiffs' injuries," the ruling read.

Families of the victims and survivors had sued the US government claiming it could have prevented the gunman from legally acquiring firearms.

The plaintiff named in the ruling was Joe Holcombe, who, along with his wife, Claryce, lost nine members of their family in the attack, including children, grandchildren and great-grandchildren.

Kelley had legally purchased weapons even though convicted felons are usually not allowed to own guns. Licensed sellers are supposed to check national databases before completing a purchase.

But the gunman was able to slip through the background check system because the US Air Force had not reported his two domestic violence convictions from five years earlier.

Air Force spokeswoman Ann Stefanek said it planned to appeal the ruling, the New York Times reported.

Gun laws in Texas are among the most lax in the United States.

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