A threat like that has to be reported to the authorities. In 99.9% of cases it’s nothing but you never know. You can’t threaten the president without getting investigated, you can’t threaten mass murder at school without getting investigated.

"A threat like that has to be reported to the authorities."

This forced reporting necessarily creates false reports. Under the law, things like terrorist threats are required to be credible or incite panic. Reporting things that aren't credible is arguably a violation of law under any other context, yet they choose to ignore that with these mandatory reporting laws. Basically it creates a situation where nobody is allowed to use their brain - automated conveyer to the criminal system.

Investigation is ok given how much shooting happens. Punishment however is way out of proportion. It was a bad joke. Does not deserve any real punishment except maybe couple of hours in a class that explains why jokes like this are bad.