Story highlights Jeremiah Oliver was last seen in September

The 5-year-old is still missing

The young boy's mother and boyfriend have been arrested

"This is a deeply concerning case of neglect," commissioner says

Five-year-old Jeremiah Oliver was last seen by his Massachusetts relatives on September 14. But the investigation into his disappearance didn't begin until last week when the authorities were first alerted to it.

Now, the child is feared dead, his mother and her boyfriend are in custody, and everyone is left wondering how a child could simply vanish unnoticed for three months.

How could this happen, especially to a child who was supposed to be receiving monthly visits from a state-provided social worker?

Turns out, tragically, Jeremiah was not getting the visits, state officials say.

Who's to blame?

The finger pointing, demands for accountability and calls for investigations are reverberating throughout the state.

"This is a deeply concerning case of neglect and abuse," said Olga Roche, commissioner of the Massachusetts Department of Children and Families. The state agency was charged with the responsibility of protecting children from child abuse.

Roche called the situation "a serious failure" and put the blame squarely on the shoulders of the boy's social worker and supervisor, both of whom were quickly fired.

"The social worker assigned to this case did not conduct the required in-person, monthly checks on the family," Roche said in a statement. "And the supervisor failed to enforce that policy."

Neither the social worker nor the supervisor have been named, but their union spokesman says they have been made "convenient scapegoats" at an overwhelmed agency.

"We are disappointed that Commissioner Roche is more interested in finger-pointing than accepting responsibility for yet another tragedy on her watch," said Jason Stephany of the Service Employees International Union Local 509, which represents caseworkers at the Department of Children and Families. "Instead, the Commissioner has chosen a convenient scapegoat to deflect blame from department administrators."

More blame to go around

But Gov. Deval Patrick hinted Friday that they might not be the only two held accountable.

"I've asked the Commissioner to look into the question about whether responsibility goes beyond those two," he said in an appearance on Boston Public Radio. "I have some reason to believe it does."

The last documentation of an interaction with Jeremiah was in May, according to Department of Children and Families spokesman Alec Loftus.

In June, Loftus says the social worker was told that Jeremiah had moved to Florida to live with his grandmother, but never bothered to follow up or verify whether that was the case.

The last time a visit to the home occurred was in November, at which Loftus says the social worker left behind a business card indicating that this would be DCF's final visit.

Just days later, on December 2, Jeremiah's 8-year-old sister disclosed to counselors at her elementary school that her mom's boyfriend, Alberto Sierra, 22, had abused her, according to a police affidavit.

Multiple calls to Sierra's attorney have gone unreturned.

"As a result of those statements" the affidavit continues, "[she] and [another brother that isn't Jeremiah] were removed from the home and taken into protective custody."

When cops asked Elsa Oliver, 28, where her third child Jeremiah was, she told them that he had moved to Florida, a law enforcement source involved in the investigation told CNN.

This time, however, she was going to have to prove it.

Where is Jeremiah?

Oliver went before a state juvenile judge at a hearing on December 13, where she 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.

The judge ordered her to produce the child within 72 hours. The time passed with no sign of Jeremiah.

Oliver was arrested.

The mother has been charged with two counts of reckless endangerment of a child and two counts of accessory after the fact of a felony (assault and battery with a dangerous weapon), according to a statement from Worcester County District Attorney Joseph Early. A plea of not guilty was entered on her behalf.

Those charges may not necessarily pertain to Jeremiah and more details could emerge at a December 24 hearing, a spokesman for the district attorney's office said.

Elsa Oliver's attorney, James Gavin Reardon, wasn't able to elaborate either.

"I met with her for 10 hours and was unable to obtain any significant information" Reardon said, prompting him to seek a mental health evaluation to determine whether she was even competent enough to stand charges.

He says that evaluation is currently underway.

Sierra, meanwhile, is charged with two counts of assault and battery with a dangerous weapon and two counts of assault and battery on a child causing bodily injury, according to the district attorney's office said.

A plea of not guilty was also entered on his behalf.

He also has a hearing scheduled for December 24.

For now, authorities are holding out hope that Jeremiah might be out there somewhere, and they're asking anyone who might know anything to call the Massachusetts State Police.