I missed a step here.
Forgive me.
At what point did Illinois return the guns?
To the father, or *anyone* for that matter?
I'd think that Illinois would have kept them.
Illinois has some procedural loophole where a relative of the listed owner of the firearms can take possession of the guns, as long as the relative has a valid Firearms Owner ID Card. It makes sense in most cases, because often seizures are prompted by red tape - delays in someone getting an FOID renewed, that sort of thing). I'm not sure that Illinois would've permanently withheld the shooter's FOID, based on an out-of-state trespassing charge.
Overall it doesn't seem like a bad provision, though I'll bet it's going to be revised soon.