This morning around 9:19 am, officers from District B-3 (Mattapan) were on patrol in the area of Norfolk Street and Peacevale Road. Officers were responding to citizen complaints of street robberies and firearm-related incidents. Officers observed a group of individuals known to police located on the above reported corner. Officers observed that all the males were wearing shorts and long sleeve t-shirts, with the exception of one, who was wearing a hooded sweatshirt. As officers continued to make observations of the group, the suspect in the hooded sweatshirt looked at officers and walk away toward Milton Avenue.As officers continued to approach, the suspect became increasingly nervous, looking back at officers, and peering up and down Norfolk Street as if he was planning to flee. The group of males began yelling “Woo Woo”, which is commonly used to warn people that the police are present. The suspect then clenched his right side and began walking fast. The suspect grabbed his right sweatshirt pocket and ran into an alley shared by 146 Norfolk Street and 5 Edson Street. While looking for the suspect, officers observed a black firearm on the roof of 146 Norfolk Street, which is the path the suspect took. The suspect was apprehended in the rear of 5 Edson Street hiding in a crawl space beneath a rear porch. A 16-year-old juvenile from Dorchester was arrested and charged with Unlawfully Carrying a Firearm, Unlawfully Carrying Ammunition, Unlawfully Carrying a Dangerous Weapon and Trespassing.