My understanding of Illinois law is that it must be either 1. not accessible, 2. disassembled, or 3. unloaded and cased.
Any one of the three makes you legal, you don’t have to do all of them.
http://www.illinoisgunpros.com/gun-in-your-car-in-illinois-without-a-carry-license-what-is-legal/
I am familiar with those guidelines. However, I have been told get a CC if you want to carry a firearm in the car...BTW, I have taken and passed the IL CC class.
IF don’t want to take class, then be smart...follow the guidelines I suggested.
Apparently firearm was accessible as it was in the car. My guess is it was reachable be driver or passenger in front seat... If it was unloaded and cased or disassembled, then there would not be an aggravated weapon charge.
They were ignorant and foolish to be at airport this week with firearm in vehicle. Oh and did not help to add a pressure cooker for the weekend of the Chicago Marathon and an AR-15...
Note the first words of your link, As long as you have a FOID* card, you can have your gun in your car.... Being a Wisconsin resident, he doesn't have one so he'd have to rely on the federal through state transportation exemption. Good luck with that. I'd go with #2 or #3 of your example. Not accessible is vague other than if locked in the trunk. And remember these things are a function of local police and prosecutor, and are defenses he'll raise at his own expense.