Jeremiah Oliver, 5, has not been seen since September. His mother's boyfriend, Alberto Sierra, 23, has been charged with assault and battery on a child, while his mother, Elsa Oliver, 28, is charged as an accessory.
Olga Roche, the commissioner of children and families, said Wednesday the social worker has been fired, the Boston Globe reported. She said the social worker apparently failed to make regular visits and had not seen Jeremiah since May.
Fitchburg residents held a candlelight vigil Wednesday evening for the boy, who is believed to be dead. Mary Santos, a neighbor, told the Boston Herald she heard screams from the home when Sierra was visiting but did not call police because she was afraid.
"I would hear terrifying screaming, banging on the walls," Santos said.
Roche's department began an investigation earlier this month after school officials said they were concerned about Jeremiah's 7-year-old sister.
Notable deaths of 2014 [PHOTOS]
JetBlue plane makes emergency landing