[Yo-Yo]

How was it possible for a felon to pass an FBI background check?

The answer is in your own question.

January, 2014 the shooter was issued an Illinois Firearm Owner’s Identification (FOID) Card.

The State of Illinois did the background check, not the FBI. Once issued an Illinois FOID card and an Illinois permit to purchase a handgun, the gun store can sell you a handgun without performing a NICS check.

[mosaicwolf]

"How was it possible for a felon to pass an FBI background check?"

Because the FBI was totally focused on Russian collusion in the 2016 election.

[Vermont Lt]

You are probably from Il, and I am not disputing what you say. But I thought the NICS check was Federal law.

[stylin19a]

According to Illinois statutes, State Police are required to check NICS database for both the FOID and gun purchase back ground checks.

http://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=1657&ChapAct=430%26nbsp%3BILCS%26nbsp%3B65%2F&ChapterID=39&ChapterName=PUBLIC%2BSAFETY&ActName=Firearm%2BOwners%2BIdentification%2BCard%2BAct.

do a search on “national instant”

FreeRegards.