Christians blaming the recent shooting on schools not allowing god.

I fail to see how not having God in schools would have caused it.

So these people are saying that God isn't omnipresent and omniscient enough to know that this was going to happen, and prevent it if that was his will?

Their reasoning is so one-sided.

No, they're saying he's omnipresent and omniscient, but petty and spiteful as well.