New York City, San Francisco and Philadelphia filed a federal lawsuit on Tuesday against the Department of Defense, arguing that an inadequate background check system has allowed many military members who should be barred from buying guns to obtain them, and was partially to blame for the mass shooting in Texas that left 26 people dead, the AP reports.

The backdrop: The Sutherland Springs shooter was convicted of domestic violence and should not have been allowed to buy a gun, but the Air Force failed to enter his name into a federal database. After the massacre, military officials acknowledged problems with the system.