(CNN) -- Massachusetts investigators said Friday they think they have found the remains of Jeremiah Oliver, a 5-year-old boy who was missing for months before police were called.
Though positive identification has not been made, Worcester County District Attorney Joseph D. Early Jr. said the body of a child found wrapped in a blanket inside a duffel bag near a central Massachusetts interstate matches the height and weight of Jeremiah.
The case of Jeremiah Oliver was the result of what Massachusetts Department of Children and Families Commissioner Olga Roche called "a serious failure."
Roche oversees the state's social workers, including those assigned to the Oliver household.
"The social worker assigned to this case did not conduct the required in-person, monthly checks on the family," Roche said in a statement when the boy was reported missing in December. "And the supervisor failed to enforce that policy."
Roche fired both of them almost immediately.
The last documentation of an interaction with Jeremiah was in May 2013, according to Department of Children and Families spokesman Alec Loftus.
In June, Loftus said, the social worker was told that Jeremiah had moved to Florida to live with his grandmother, but did not follow up or verify that.
The last visit to the home was in November, at which the social worker left behind a business card indicating it would be the Department of Children and Families' final visit, Loftus said.
On December 2, Jeremiah's 8-year-old sister told counselors at her elementary school that her mother's boyfriend, Alberto Sierra, 22, had abused her, according to a police affidavit.
After those statements, the girl and another brother were taken into protective custody, according to the affidavit.
When police asked Elsa Oliver, 28, where her third child, Jeremiah, was, she told them he had moved to Florida, a law enforcement source involved in the investigation told CNN at the time.
At a December 13 hearing before a state juvenile judge, Oliver was "observed to have bruises, disheveled hair, and appeared to have been assaulted," according to court documents. She refused to divulge Jeremiah's whereabouts, according to the source, so she was arrested.
In March, Oliver and Sierra, both of whom have been in custody since December, were indicted by a grand jury on charges related to Jeremiah's disappearance, as well as on charges of child abuse.
Calls to the attorneys for both were not immediately returned Friday.
An autopsy on the remains found Friday is expected to be completed over the weekend.
CNN's Lawrence Crook III and Dave Stewart contributed to this report.