The incident happened around noon Sunday inside an apartment complex on Nepperhan Avenue in Yonkers.
Arriving officers found the boy, identified as Nyran Plummer, on the bedroom floor and performed CPR along with members of the Yonkers Fire Department and Empress Emergency Medical Services.
Nyran was rushed to a local area hospital, where he died days later.
His family told Eyewitness News that they have no idea where the gun came from or how Nyran got it.
Medical examination of his head indicated that he suffered an apparent self-inflicted gunshot wound to his right temple.
Officials say the preliminary investigation has determined that the victim was home alone with a younger neighbor in separate rooms, and at some point, the victim discovered or came into possession of a loaded handgun and discharged two cartridges in the bedroom.
One bullet reportedly struck a window, while the other struck Nyran.
The victim was located by adults and family members a short time later. The younger neighbor was uninjured and uninvolved, and there are no other reports of injuries.
First responders located an illegal, loaded .25-caliber semi-automatic pistol at the scene.
Investigators are working to determine how the handgun came to be possessed by a child, and the weapon's origins and transfer history.
The investigation is active and ongoing, and additional information may be released as it becomes available.