• Last week, there were at least 30 hoax threats about a school shooting or other violence on campuses across the country.
  • The FBI is examining whether some of the threats are connected but experts say such hoaxes can have dangerous consequences.
  • Students and parents expressed fear as schools were placed on lockdown.

Across the country, dozens of schools went on lockdown. Students and teachers hid in classrooms. Police searched campuses. Parents panicked.

Each time, there was no threat. Officials say there’s been a wave of false reports of school shootings and threats of violence over the last several days. USA TODAY found at least 30 active shooter false alarms and threats made at schools last week.

Authorities haven’t publicly said the incidents are related, but experts say these intentional false reports have similarities. Their origins can be difficult or impossible to trace, but waves of false alarms are often the work of disgruntled pranksters trying to disrupt school or malicious bad actors trying to sow fear. And such hoaxes seem to increase around this time of year with students returning to classrooms. 

“A red flag… is when you start seeing a chunk of these very similar threats in multiple cities in one area or region or state, and then others in another state. It’s usually a red flag for what they call swatting,” said Kenneth Trump, a school safety expert.  

“Swatting” is making a hoax call to law enforcement to deliberately cause a large police or SWAT team response. Sometimes, an individual does it to single out someone specific, but the calls can also be done in waves as a trend to seemingly random targets.

MORE ON SHOOTINGS:Mass killings database reveals trends, details and anguish in every US event since 2006

INCREASED VIOLENCE:Shots fired in US schools spiked dramatically last year, gun violence report finds

False school shooting reports in Florida, California and more

In Texas on Tuesday, Houston authorities received a call that said two shooters were rampaging Heights High School and 10 students had been shot. Police did a room-by-room search of the school. They found no trace of a shooting.