With the video in the room, I'm willing to bet a pretty penny that he recorded a manifesto at some point.
Look, people don't go to this trouble and then fail to explain the most important part---- why?
He saw this as a teaching moment (I'm guessing) and what's a teaching moment without a lesson? The teaching lesson will be found either on the note left on the table that you can clearly see, or by a pre-recorded video of him prior to the shooting.
Look at the meticulous details this guy worked through-
Systematically stocked up on guns and ammo from multiple different dealers so as not to raise any eye brows. Buying 40ish guns from one dude looks....... suspicious. Buying them from multiple dealers, not as much.
He picked the perfect firing point venue.
He picked the date based on an open air event held just beneath his firing venue.
He set up monitoring cams to know when the cops arrived at his door.
He altered semi-auto weapons to function as fully auto.
He was able to smuggle an arsenal into his hotel room and keep it hidden from staff.
He erected two firing nests that provided him with a perfect firing vantage point.
He brought an industrial hammer to smash out the windows.
Seriously........ look at these fvcking details...... you can't convince me that he didn't record a manifesto prior to launching this attack.
This is calculated behavior and NOT providing US, his "audience", a reason or justification for his actions would not book end his evil masterpiece.
"What's in the box!?!?!" remember that?