Victim identified as Savion Ellis.
Boston Police report finding a 12-year-old with a fatal gunshot wound at 35 Fessenden St. around 2:05 p.m.
Stanley Staco reports he was shot in the chest.
Walter Hendrick, 22, of Mattapan, was arrested on charges that include improper storage of a firearm to which somebody under 18 could gain access, police say.
Police add Hendrick, scheduled for arraignment Friday in Dorchester Municipal Court, was also charged with illegal possession of a firearm and illegal possession of ammunition.
Fessenden Street is about a half mile from where 13-year-old Tyler Lawrence was murdered in January.
In 2014, a 14-year-old playing with a gun shot his 9-year-old brother to death on Morton Street.