Princeton Police File Photo

A Princeton Police car in this file photo.

(Keith Brown/The Times)

PRINCETON - Princeton schools were ordered to "shelter in place" Tuesday after John Witherspoon Middle School received a pre-recorded message from a woman claiming to have a weapon and threatening to harm children, school officials said.

The message, which came in a 9:45 a.m., was identical to one received at Riverside Elementary School two weeks ago, Superintendent Steve Cochrane said.

Police were immediately notified and all schools were told to "shelter in place," which means students are kept indoors and heightened levels of security are maintained.

"Our police do not believe there is a credible threat today at John Witherspoon or any other school in Princeton," Cochrane wrote in a letter to parents and staff. "The police are, however, remaining on site at JW through the remainder of the day and will have a presence at each of our other schools as well."

Dismissal and after-school activities will go on as normal.

The incident remains under investigation, but police believe it was a case of "swatting," which involves contacting an individual or institution with a false report designed to elicit a response from a SWAT team.

Cochrane said that there have been a number of similar false reports in Monmouth County in the past two weeks, and the police are coordinating with other agencies to actively investigate them.

Indian Hill School in Holmdel was placed under lockdown Tuesday following a "swatting" incident.

Under a proposed new bill, the crime would be punishable by a term of imprisonment of five to 10 years, a fine of up to $150,000, or both.

Cristina Rojas may be reached at crojas@njadvancemedia.com. Follow her on Twitter @CristinaRojasTT. Find The Times of Trenton on Facebook.