If Cruz had been a frequent visitor to any federal agency office to complain about whatever, and the FBI had received this call - well, then it would've been dealt with immediately as an "escalating threat". But just some school kids and teachers at risk? Meh.
Right, if she really expected them to investigate the risk, she should have brought it to their home turf. Had she heard him say he will, “ turn the local Eff-Bee-Aye office into swiss cheese,” they would have been at his doorstep within the hour.