NEWTOWN, Conn. (CBSNewYork/AP) — A Newtown, Conn. elementary school was placed on lockdown Tuesday over unspecified threats.

Most schools in Newtown opened on Tuesday, four days after a gunman fatally shot 20 children and six adults at Sandy Hook Elementary School.

In a letter to parents published by WFSB-TV, Principal Barbara Gasparine said students at Head O’Meadow Elementary School should stay home because police were prepared to have the school in lockdown.

“As was predicted by the police that there would be some threats, the police were prepared and have us in lockdown, which is our normal procedure. Due to the situation, students will not come to school today. Please make arrangements to keep them home. All-Star has been notified and will return any students already picked up.”

School officials said the lockdown was normal procedure because some threats were predicted by police.

All other schools in town, except Sandy Hook, opened on Tuesday.

Police stepped up security in the area as thousands of Newtown students returned to class for the first time since Friday’s mass shooting at Sandy Hook Elementary School.

“Be assured that the safety of your children and our staff are our first priority,” Superintendent Janet Robinson said in an email to parents.

Sandy Hook Elementary remains closed indefinitely.

(TM and Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

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