The FBI's background-check system is missing millions of records of criminal convictions, mental illness diagnoses and other flags that would keep guns out of potentially dangerous hands. Experts who study the data say government agencies responsible for maintaining such records have long failed to forward them into federal databases used for gun background checks. As the shooting at a Texas church on Sunday showed, what the FBI doesn't know can get people killed. In that case, the gunman had been convicted at a court-martial of charges stemming from a domestic violence case. Officials say the Air Force never notified the FBI of his conviction, so when he purchased weapons at a retail store, he cleared the background check. The FBI said it doesn't know the scope of the problem, but the National Rifle Association says about 7 million records are absent from the system, based on a 2013 report [which] determined that at least 25% of felony convictions "are not available" to the National Instant Criminal Background Check System maintained by the FBI. In light of the Texas shooting, Air Force officials have ... faulted the staff at an air base for not sending the necessary information to the FBI, but federal officials who work in the database effort say the problem of military nonreporting of domestic violence cases extends far beyond a single base or service branch. A large number of people convicted of misdemeanor domestic violence - who also are prohibited from buying guns - are absent from the FBI database as well.