Devin Patrick Kelley, who had a history of domestic abuse and mental health problems, killed 26 people and wounded 20 others at the First Baptist Church in Sutherland Springs, Texas.
The victims included one-year-old Noah Holcombe and his aunt 36-year-old Crystal Holcombe, who was pregnant and died along with three of her five children. In all, the Holcombe family counted nine members who perished in the attack.
The lawsuit was filed by Joe and Claryce Holcombe, who are in their mid-80s and lost their 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 prior to completing a purchase.
But Kelley 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.
"The utterly careless and reckless failures of the US Air Force to satisfy their reporting obligations... resulted in numerous missed opportunities for various local law enforcement agencies to prevent further violence by Kelley," the lawsuit claimed.
In a subsequent review, the Air Force found dozens of other cases in which criminal convictions had not been properly reported to law enforcement databases.
The Pentagon's Inspector General revealed in December that an evaluation of military police across all the services found that they often failed to update a federal database with the fingerprints and outcomes of military criminal convictions.
The US Air Force did not immediately return a request for comment regarding the lawsuit.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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