Jericho high school and middle schools are on high alert while authorities are investigating a bomb threat Monday.

A Nassau County police spokeswoman said a search of the school buildings did not uncover anything suspicious.

“Several high school students have recently received emails and text messages regarding a possible bomb threat,” Henry Grishman, superintendent of the Jericho school district, said in a letter to parents.

He wrote that the district believes they know who is responsible for the threats and they are working with police.

The schools are on lockdown and students were searched upon entry as a precaution.