Story highlights Teacher Jason Adams has a concealed firearms permit, but it is illegal to have a weapon on school grounds

Adams, who hasn't commented, faces a felony charge for having the gun

School system says the case is "very serious and troubling"

(CNN) A teacher in the Connecticut town that was site of one of the deadliest school shootings in U.S. history was arrested Wednesday after police say he brought a gun onto school grounds.

Jason M. Adams, a teacher at Newtown Middle School, was carrying a concealed firearm for which he had a permit, Newtown police said. He was stopped inside the school by security personnel Wednesday before 9 a.m., the Newtown Public School District and police said.

Newtown police said Adams faces a charge of possession of a weapon on school grounds , a Class D felony, according to Connecticut law.

Adams, who was released after processing, did not reply to CNN's requests for comment. Adams was placed on administrative leave, the school system said. He will appear in court on April 20.

"This matter is very serious and troubling," Newtown schools said. "The Newtown Police Department is confident that security precautions put in place prior to the incident were instrumental in the quick and appropriate response to the event."

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