That ship has sailed. The media was immediately accusatory toward the school and church where the shooter attended classes. So was the LGBTQ community, equally accusatory toward the school and church. AJMOOOh for sure, you're right, a potential criminal doesn't need a manifesto from another criminal in order to do bad deeds.
It's just that the media coverage of these shootings is so sensational, that it tends to attract like-minded folks who think they, too, might get revenge in a similar manner.
My only concern is making it look as though the perp has any sort of valid gripe against society. I just hate seeing the shooters (even if they're dead) get that much attention. Because I think lot of them are seeking that attention.