CHICAGO (CBS) — Three Evanston Township High School students are facing criminal charges, a day after the school was locked down for hours when officials found two guns in the building.

No shots were fired and no students were injured during the incident, which prompted authorities to lock down the school for most of the school day on Thursday as police investigated.

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Police said it all began around 9:30 a.m. when an Evanston Police school resource officer was made aware of students potentially smoking marijuana in a bathroom.

When that officer and members of the school safety team went to investigate, police say two students were immediately detained for smoking, and during that investigation they also found two handguns, which triggered the hours-long lockdown.

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Police said security footage later revealed seven other students previously had been in the bathroom as well, and were detained.

Friday afternoon, police said two 16-year-old boys had been charged as juveniles with felony aggravated use of a weapon on school grounds. Another 16-year-old boy was charged as a juvenile with misdemeanor cannabis possession.

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The other six students who were detained have been released without charges.

CBS 2 Chicago Staff