That sounds almost plausible. But why would the suspension be for only three days? That’s like announcing to the retributive friends when the kid will be ripe for revenge.
Three reasons: First three days is a pretty adequate cooling off time period. Second that is plenty of time to view video tapes, if the bus had cameras, or cell phone recordings that made it on to youtube.
It also gives the school and the police time to do a more formal investigation.
I noticed that the gunman was initially charged with a relatively minor offense. Once they get all the evidence they can bump this up. If they charge him with attempted murder right off the bat and that can't stick the DA is less likely to charge him with the lesser included and he walks on all counts and becomes a hero.