A cell phone allegedly used to make a threat to Fairfax High School has been confiscated by Fairfax City Police detectives. The threat was posted on Twitter by someone who appeared to be a student angry over being suspended.

Sgt. Shawn Sutherland said "persons of interest" had been identified and interviewed and that a search warrant had been filed on the confiscated cell phone. The investigation is continuing.

(Photo: Fairfax County Police)

At the school on Thursday, a large number of students apparently stayed home.

Extra police officers and FBI agents were on hand to ease people's minds.

For mother Horalda Pinto, she said her daughter wanted to go to school, but was nervous.

"I let her come to school and I went to work, but she's been texting me every hour. She said that there was a lot of cops and SWAT Team," Pinto said, adding that her daughter was afraid of what might happen. "How could you not be afraid?"

PREVIOUS: Two Maryland students arrested for making threats, guns found in home

So, how are school systems responding to the new changing landscape of threats on social media?

"We investigate immediately," said Jane Strauss, chairwoman on the Fairfax County School Board.

"We live in an era, particularly since last week, where you don't know if the text message, is it real? Is it being amplified by a bot? Is it being sent out to increase fear?" Strauss said.

PREVIOUS: Two Virginia schools threatened on social media

"As we investigate threats, law enforcement will visit the student in his or her home and do a real threat assessment and say, is it real, is it not, what does this child need? And, if appropriate, they will search the home for weapons or firearms," said Stauss.

When a threat is posted that names a school, it gets spread and fear escalates.

"That's right and we will have on any given week, we will have ongoing investigations... but our own students are very, very helpful. But right now, we need to calm this fear. We are on top of it, and we will keep our kids safe," said Strauss.

In the Fairfax High School threat, police said no weapons were found in the home to connect a real threat.