CHICAGO (CBS) — Illinois State Police have said they now know how the gunman in the deadly mass shooting at an Aurora factory was able to pass a background check for a Firearm Owner’s Identification card, despite a felony conviction in Mississippi.

State police said, when Gary Martin applied for a Firearm Owner’s Identification card in 2014, their criminal background check did not reveal his 1995 conviction for aggravated assault in Mississippi.

The conviction wasn’t discovered until five days later, in a new background check after Martin applied for a concealed carry license, and submitted his fingerprints to speed up the application.

Illinois State Police revealed Martin’s Mississippi arrest did not show up in databases, because his Mississippi state identification number did not appear in databases until Thursday, more than two decades after he pleaded guilty to aggravated assault involving a former girlfriend.

State police also acknowledged lapses in enforcement of FOID card laws, after a review of how Martin was allowed to keep his gun after his FOID card was revoked. That gun was the weapon Martin used to kill five people and wound six others at the Henry Pratt Company plant in Aurora last week.

After state authorities learned of Martin’s felony conviction in 2014, police revoked his FOID card, and sent him a letter stating he needed to relinquish his gun and license.

However, Illinois State Police said they have no record they notified the Aurora Police Department that Martin’s FOID card had been revoked.

While that doesn’t mean a letter was not sent to Aurora police, as the state keeps such records for only three years, Aurora police have said they also have no records they were notified Martin’s FOID card had been revoked.

According to data provided by Illinois State Police, such lapses in returning a revoked FOID card or surrendering a weapon as required are all too common.

More than 10,000 FOID cards were revoked last year, according to Illinois State Police. Whenever a FOID card is revoked, the state requires the license holder to submit a “Firearm Disposition Record” notifying police they have disposed of any weapons they owned. However, in more than 75 percent of the cases last year when a FOID card was revoked, license holders never told police they had surrendered their weapons.

From 2014 through 2019, only 110 people were arrested for failing to return a revoked FOID card or failing to submit a “Firearm Disposition Record”.

Last year, there were only 10 such arrests statewide.