Unlike TruBluKentuckian and the other adults on this thread, I'm sure you will obsess over that question ad nauseam.
I’m thinking they’re trying to figure out if the shooter acted alone. They’re probably also going through his computer and phone records with a fine tooth comb. I realize that this will take time.
I was thinking that by now the investigators could at least say (for sure) he did kill himself, he did/didn’t leave a suicide note, they do/don’t have security camera video of him hauling the weapons up to the room, etc.