Stamford High School is up and running after officials received an unspecified threat on Thursday.
Assistant Police Chief James Matheny said the school was searched with officers and K-9 dogs around 4 a.m. Friday in an abundance of caution.
"The sweep came up clean, with nothing found," he said.
Matheny would not describe exactly what the threat was, or where it appeared, due to an ongoing criminal investigation.
At least one K-9 and an officer will remain on scene until the afternoon.
"We have a great working relationship with school officials and everything is running smoothly," he added.
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