The mentally ill, substance abusers, and other dangerous individuals have freely purchased firearms because nearly 90% of states fail to send all necessary information to a federal database used to run background checks for gun buyers, according to a new report.

The findings come from a new report, "Fatal Gaps," produced by the anti-gun advocacy group Mayors Against Illegal Guns.

The report showed that 23 states submitted fewer than 100 mental health histories to the National Instant Criminal Background Check System (NICS). The database has blocked more than 1.6 million gun-permit applications and sales to felons since it was created in 1999.

The report cites Virginia Tech shooter Seung Hui Cho and Tucson shooter Jared Loughner as prime examples of the reporting failure.

Even though a judge had found Cho to be mentally ill two years before his 2007 rampage, the information never made it into the NICS. Cho was able to pass several background checks to buy the guns he used to kill 32 people and then end his life, according to the report.

Before killing six people and critically wounding 13 others, including Rep. Gabrielle Giffords, at a Tucson shopping center, Loughner had a troubled past that included a drug-related arrest, an admission of drug use to the U.S. Army and suspension from community college for a pattern of disturbing behavior.

Read the full report here.

By Paul Clinton