Greenwich High School was placed on lockdown Thursday morning after a 911 call reporting a student with a gun walking into the building.
Police received the call at 10:43 a.m. from a student who reported an armed male student was entering the high school.
Greenwich police, including the Department's school resource officer, responded and detained the suspected student at gunpoint, according to police.
The student, who was identified as Gianfranco Romero, 19, was 'highly cooperative" and did not have a weapon in his possession, police said.
After speaking to witnesses, police determined Romero made a comment to two other students that he had a gun in his book bag and that he planned to use the gun to shoot people in another state, according to investigators.
The students became alarmed and talked to other students, who then made the 911 call to police.
Romero was arrested and charged with breach of peace.
A search of Romero's house did not turn up any weapons, police said.