SAN ANTONIO (Reuters) - A couple whose nine relatives were among the 26 people fatally shot in a Texas church massacre in November has sued the U.S. government for $50 million, saying its “institutional failures” played a part in the murders, court filings on Friday showed.

Devin Patrick Kelley, 26, of Braunfels, Texas, U.S., involved in the First Baptist Church shooting in Sutherland Springs, Texas, is shown in this undated Texas Department of Safety driver license photo, provided November 6, 2017. Texas Department of Safety/Handout via REUTERS

The lawsuit filed this week in federal court in Texas and made public on Friday said the U.S. Air Force acted negligently when it failed to report the criminal record of gunman Devin Kelley to a U.S. database, which could have prevented him from legally purchasing an assault rifle used in the killings.

Air Force officials were not immediately available for comment but have previously said they do not comment on specific claims.

Legal experts have said the Air Force would not be able to claim federal immunity in the case, but cautioned any lawsuits faced a prolonged battle.

The lawsuit was filed on behalf of the parents of Bryan Holcombe, who was near the pulpit of the small church in Sutherland Springs when Kelley opened fire.

Holcombe was shot in the back and died on the church’s floor. The family lost eight other members in the attack.

Kelley was convicted about five years ago by a general court-martial of assaulting his then-wife and stepson while he was in the Air Force, offenses that made it illegal for him to possess a firearm.

“But Airman Kelley was able to purchase an assault-style rifle as a direct result of the U.S. Air Force’s admitted, systemic and longstanding failure to comply with the law and its own internal policies, regulations, and guidelines,” the lawsuit stated.

The Air Force said in a statement on Nov. 7 it did not enter that information into a federal database used in background checks for firearms purchases, something it was legally required to do.

The information should have been filed in the National Instant Criminal Background Check System (NICS), and indicted that Kelley was ineligible to buy a firearm, the lawsuit said.

In March, U.S. President Donald Trump signed an act to improve federal background checks for gun purchases. The bill, called the Fix NICS Act, would ensure that states and federal agencies comply with existing law on reporting criminal history records to the national background check system.