The Ponchatoula Police Department investigated on Tuesday two threatening letters received by elementary school principals Monday.

The letters, which contained vague threats not directed to anyone in particular, were mailed to the principals of Tucker and Perrin elementary schools, both in Ponchatoula, Police Chief Bry Layrisson said Tuesday.

The letters are “very similar in nature” and appear to be from the same person or people, Layrisson said.

The threats do not appear to be connected to Friday’s shooting at Sandy Hook Elementary School in Newtown, Conn., he said.

The incident was being treated as a criminal investigation, and police were working with school officials and other law enforcement agencies to track down the perpetrators, Layrisson said.

Tangipahoa Parish Schools Superintendent Mark Kolwe said the district’s schools were on a heightened state of urgency and awareness, but had not been placed on lockdown.