FREDERICK COUNTY, Md. (DC News Now) — A 16-year-old boy was arrested by officers from the Frederick Police Department after a team found an unregistered AR-15-style pistol in his bedroom.

Police executed a search warrant on Monday at a home in the 5900 block of Jefferson Commons Way. The warrant was related to an ongoing investigation into an armed robbery that happened in July.

Detectives found the pistol with two fully loaded magazines in the bedroom of the 16-year-old suspect.

The boy was arrested and taken to the Frederick County Adult Detention Center and will be charged as an adult.

He faces charges for possession of a regulated firearm by a minor and possession of a firearm without a serial number.