A gun discharged Thursday inside the backpack of a 9-year-old in Maryland while the student was in school, following a similar incident days earlier in Virginia. 

The incident occurred in southern Maryland, at Billingsley Elementary School, according to a Washington NBC News affiliate.

A school resource officer and teacher said they recovered the gun right after it went off. 

The Charles County Sheriff's Office is investigating the situation.

Three days earlier, a handgun went off in a third-grader's backpack at a school in Virginia.