Was just about to say this.

I'm honestly surprised this hasn't happened before; but willing to bet that since it's clear that the US has no intention of addressing the problem it will probably be pretty common for bad actors outside the US will engage in this tactic.

Now that bad actors in foreign countries know that the US doesn't give a fuck about children being slaughtered, they'll engage in these sorts of hoaxes to disrupt the lives of citizens and create situations where people become complacent to the threats that allow more mass shootings to happen.