Ok. Sounds like was part of the op, not a lone wolf.
There's been a lot of false reports - reporters can't even get which vehicle he drove right -car or truck....let alone how this all unfolded. So it misleads people into thinking what they should not until there's an investigation.
If you watch the video of him entering the school , that's not been slowed down, clearly he “ran” into the school and was on the run. But if you go by the slow downed version it looks like he just walked in. So people get the wrong impressions all the time.