A Newtown, Connecticut, middle school teacher is under arrest after police said witnesses saw him with a gun on school property. 

Jason Adams, 46, of Newtown, possesses a valid state pistol permit, but both state law and Newtown Middle School rules ban guns on campus, police said. 

After a brief detention by school security officials Wednesday morning, police arrived and charged Adams with possession of a weapon on school grounds, authorities said. 

Adams was released on his own recognizance and is due back in court in Danbury on April 20. The teacher was also placed on administrative leave, pending the school’s own investigation. 

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“This matter is very serious and troubling, both the Newtown Public School system and the Newtown Police Department took immediate steps to address the matter,” a statement released by the school district read. “Both agencies have been working closely together to investigate the incident and are taking precautions to ensure the continued safety of our students, staff and community members.”

Newtown was the site of one of the country’s worst mass shootings in history, when 20-year-old Adam Lanza fatally shot 20 students and six staff members at Sandy Hook Elementary School in 2012.