"We have to be more vigilant with younger kids. Obviously they can't speak for themselves, report abuse, or protect themselves," Parello said.
She said it was premature to conclude whether state workers responded appropriately.
"We can't make a judgment," she said. "This is a horrific, awful tragedy. The nature of it is just so awful, but we have to be careful not to indict the whole system." That's why a review is needed, she said.
Commissioner Allison Blake of the Department of Children and Families did not return calls seeking comment. The department has been under the supervision of a federal judge since 2003 after high-profile lapses in oversight.
The state spent $1 billion on changes after the mummified remains of a 7-year-old boy were found in the basement of a Newark apartment and four boys in Collingswood were found starving because their adoptive parents withheld food.
Gov. Christie appointed Blake to oversee the department in 2010, and Parello said there had been significant improvements and transparency since. She said she hoped for transparency in the Thomas case.
On Wednesday, Blake's office issued a news release confirming, among other things, that there was an open case involving Thomas, a 1996 graduate of Northeast High School in Philadelphia. A message under the yearbook picture of a smiling Thomas with pearls draped around her neck said, "Thank you Mom for all your support."
Thomas called 911 about 12:30 a.m. Wednesday to report that her son had been stabbed. In a six-minute recording of the call, Thomas sounded coherent as she said her son had been stabbed. At first she said her boyfriend did it, but then she admitted, "I did it."
Asked whether she took medication, she responded that she took the antidepressant Prozac. She said she had not taken it that day but should have.
When police arrived at Thomas' Parkside apartment in the 1400 block of Kaighns Avenue, they found the boy's torso on the first floor and his head in the freezer. In a second-floor bedroom, Thomas fatally drove a knife into her neck. She also had a stab wound to her chest, authorities said.
Autopsy results released Thursday showed that Zahree was alive when he was decapitated. Thomas died from the neck wound.
Jason Laughlin, a spokesman for the Camden County Prosecutor's Office, said that there was evidence of drug use by Thomas but that it would be several weeks before blood-test results were available.
In November 2010, Thomas was charged with endangering the welfare of a child after she told police she smoked marijuana laced with the hallucinogen PCP (phencyclidine), known to cause violence in some users, according to court records.
Police found her screaming in the street and took her to Cooper University Hospital, Laughlin said. She told them she could not remember where she left her baby, records show.
Laughlin said police found the child with a neighbor who said she took the boy out of a car but did not know where the child's mother was. In November 2011, the neighbor recanted, and prosecutors dismissed the criminal charge.
Camden County Prosecutor Warren Faulk said child welfare workers were notified. He said that he spoke with officials with the state on Wednesday as authorities reviewed how the case was handled. After the arrest, Zahree was placed in his maternal grandmother's care. authorities said. On April 3, a judge returned custody to Thomas.
In the state's news release issued Wednesday evening, the agency reported that support from "the community and state agencies were extensive and included therapeutic reunification services, individual counseling and medication monitoring, substance-abuse testing and treatment, parental capacity evaluation, post-reunification services, job training, and child care."
"Our staff visited with the family regularly, and was in communication with all service providers."
On Thursday, a spokeswoman said no additional details were being released.
The case comes a month after a report from a federal court monitor showed that social worker caseloads at the Department of Children and Families were starting to rise and that only 55 percent of children put in foster care placement had two documented visits by caseworkers each month, the number mandated by the federal settlement.
"The monitor continues to be very concerned by this low performance given the importance of visitation by caseworkers during the first few months of placement to assess children and families' needs and to ensure stability," the report states.
The state Legislature cut $11.5 million from the 2013 DCF budget.
Parello said the agency's response Wednesday to the Thomas case lacked details as to how often workers visited Thomas, when they last saw her, and how they monitored her medication and drug use.
"If she was on Prozac and then was out smoking PCP, that's a recipe for disaster," Parello said. "We're going to request some information. We don't always request it, but this is a very concerning case."
Contact Barbara Boyer at 856-779-3838 or email@example.com.
Inquirer staff writer Darran Simon contributed to this article, which also contains information from the Associated Press.