The TSA said in a statement that it is investigating the matter “to determine what occurred and what steps, if any, need to be taken to ensure that security protocols are executed appropriately.”
If we accept the premise, for now, that TSA is going to do precisely this ... how, exactly, can TSA figure out "what occurred"?
If TSA can figure out when the passenger passed through a checkpoint, and if TSA can figure out which checkpoint and screening line, and if the videotape at the checkpoint is working so that the exact moment of screening can be found, what's the videotape going to reveal? Will it be detailed enough to figure out which TSOs handled the backpack, or were viewing the X-ray images? Will it be detailed enough to show what image the backpack made on the X-ray screen?
In short ... even if you didn't have TSOs frantically trying to make sure that they're not blamed for this, I'm not sure how TSA could figure out anything that would allow them to take specific corrective actions.