It's not a disclosure issue. There just isn't as much out there. Crooks used a VPN, was careful, etc. The MN shooter literally posted a 250+ page hand-written diary in a 20-minute YouTube video. The two couldn't be any different with how they operated.
I get that. I'm a little more willing to believe he covered his tracks well based on his SAT score - clearly bright - but I also know the kind of forensics that can be performed (in cases like this) and we sure haven't heard what that revealed. Hell, we don't even have a medical report on the ear.
Ie there is definitely a disclosure issue