While NICS is a federally implemented system, its effectiveness relies heavily on state participation. State compliance in supplying records varies, partly because not all states have achieved fully computerized record-keeping. Since 2008, with the passage of a Brady bill amendment in the wake of the 2007 Virginia Tech massacre, the federal government has increased funding for states to digitize their criminal records. Since then, database submissions have increased [source: FBI].
But certain types of records are widely withheld. That amendment, the NICS Improvement Amendments Act (NIAA), was most notably aimed at increasing the provision of mental health records not generated by court proceedings. The 2007 Virginia Tech shooter had a documented history of mental-illness-related hospital visits, including a night spent in a psych ward, that didn't show up in the background check performed before he legally purchased the guns he used to shoot 32 people and himself [source: Friedman].
But the goal of expanding the mental-health records available to NICS is complicated by another, older act: the 1996 Health Insurance Portability and Accountability Act, or HIPAA. Part of HIPAA protects the privacy of patient medical records, limits who has the right to see them, and gives patients greater control in deciding who's allowed to access their histories [source: U.S. Dept. of Health & Human Services].
In some specific cases, HIPAA allows for health information to be released to law-enforcement authorities without the patient's consent -- records indicating child abuse or domestic violence, the location of a fugitive of justice, or elements of a crime, for instance [source: U.S. Dept. of Health & Human Services].
Firearm background checks are not among HIPAA's list of privacy exceptions, and states decide for themselves whether to allow NICS access to protected mental-health records. The NIAA seeks to increase provision of mental-health-related records by tying them to federal funding of state law-enforcement activities. Some states have responded by feeding more health records into the system. Others have deferred to HIPAA and still keep them private. In 2012, a federal review showed 17 states had contributed less than 10 mental health records to NICS [source: Pickler].
The absence of comprehensive mental-health records in the NICS places significant limits on the efficacy of background checks; but of the 100,000 annual gun-related casualties in the United States, relatively few of them are at the hands of mentally ill mass-murderers. There's a far greater loophole in the background check system.