The threat was discovered in the noon hour and school officials acted quickly, Greenwich Police Lt. Kraig Gray said.
"It was kind of specific to a time and location and that time was, when it was brought to the attention of school security, was coming quickly," Gray said. "Pretty quickly it became a decision had to be made and in the best interests of public safety as well as everybody that was here they called a lockdown."
Gray said the writing in a girls' bathroom did contain a threat of violence but he didn't give any more details.
Last week, there were similar types of written threats Darien High School that warned students about attending school on a specific time and date, but Gray declined to make any connection with those incidents.
He also declined comment on whether police seized any contraband during their search of the students and the every classroom. Gray said the investigation was continuing.
"Hopefully we get to the bottom of this because we are taking this very seriously," he said. "This kind of threat communicated inside the school grounds is something that nobody should play around with."
Police officers practice situations similar to what had occurred Wednesday, Gray said. Greenwich Public Schools also practice those situations, he said.
"There was plenty of cooperation amongst obviously the police department and the administrative staff here," he said. "Students also did a great job and very happy with that and they did what they were supposed to do."
He also praised parents for their understanding during the lockdown.
"They were very patient and they put their trust in the Greenwich Police Department and the Board of Ed. that we were going to take care of their kids."
Superintendent of Schools Sal Corda praised the work of everyone involved and promised the investigation would continue.
"Our procedures were implemented and students did an outstanding job in following the directions of the staff," he said in a release. "The high school administration and the staff acted with a high level of professionalism and evidenced the strongest of concerns for student safety at every step of the process."
He also praised Greenwich Police for their work and "imposing presence" as they worked with staff and ensured a smooth process.
"Every room was thoroughly searched and every student was appropriate searched by a male or female member of the high school staff," Corda said.
All of the other schools in town were dismissed at their regular times.
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