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A man who killed five people in Aurora last week should never have been able to buy the gun he used in the mass shooting, and WGN Investigates finds there may be a lot of other people falling through cracks in Illinois’ gun laws.

Anyone looking to own or purchase a firearm in Illinois is required to have a valid Firearm Owners Identification (FOID). Illinois State Police said Aurora shooter Gary Martin lied on a FOID application in 2014, stating he did not have a felony conviction. A records search failed to reveal that Martin was actually convicted of aggravated assault in Mississippi in 1995 for an attack that reportedly nearly killed his girlfriend.

WGN Investigates was able to trace his convictions with a simple internet search, but how the error got past Illinois State Police is unclear. Receiving the FOID card allowed Martin to purchase the Smith and Wesson handgun used in the Aurora massacre.

It wasn’t until two months later that authorities realized he shouldn’t have a FOID card. It was revoked in March of 2014 after Martin applied for a concealed carry permit, submitting a fingerprint with the application, and a records search revealed the out-of-state felony conviction.

Illinois State Police denied his application and revoked the mistakenly-issued gun license. As part of the process, they sent Martin a letter telling him to turn over his weapons, or give them to someone with a valid FOID card. After that, police say they never received a response indicating he received the notification or acquiesced with their orders.

WGN Investigates found in 2014 alone, 6,461 people also had their cards revoked in Illinois. From the start of 2014 to today, the total is over 48,000, and each one received similar letters ordering them to relinquish any weapons. The question is: what happened to their guns?

Michael Johnson, a criminal defense attorney who also represents persons applying for FOID cards and conceal carry licenses, says what happens next is up to the gun owners.

“You’ve got to trust them,” Johnson said.

Other cities and states are addressing the lack of follow-through. Seattle has tried to close loopholes by using courts and law enforcement to knock on doors and confiscate weapons. California has a designated law enforcement team to do the same thing.

Illinois legislators tried to make a change in 2016 requiring police to go to the homes of those who’ve had their FOID cards revoked and look for weapons. It failed because lawmakers were worried it would overtax police departments.

A new state law taking effect in Illinois says anyone can report someone to law enforcement if they think that person shouldn’t have a weapon.

“There is a new statute that came out this year, that if you even have some concern about an individual you can file a petition that you think this person is dangerous, has a mental illness, violent tendency, it could even be a police officer, and you file a petition that his FOID or Conceal Carry be pulled,” Johnson said.

Further complicating the issue, government agencies sometimes fail to report when an individual should have their FOID card revoked. Courts and police departments are supposed to report such instances to the Illinois State Police, such as in domestic violence cases, DUIs, assault charges, or if a court finds someone mentally incompetent.

An inspector general’s report from one year ago did find Chicago police often failed to provide the Illinois State Police with information from arrests needed to deny or revoke a FOID card, and officials are reportedly working to improve the process.

In the case of domestic violence, a judge can order an offender to turn over all their weapons and their FOID card. In the Mercy Hospital shooting, a former girlfriend had filed for an order of protection against shooter Juan Lopez. Lopez reportedly held a valid firearm owner’s identification card and concealed carry license at the time of the shooting. He legally purchased at least four guns in the last five years, according to the Tribune.

WGN Investigates was unable to find to what degree this is happening, or how many are reported to state police. We requested that information earlier this month and have not heard back.