Toxicology tests have confirmed that the Camden mother who decapitated her toddler and killed herself in August had smoked marijuana laced with PCP.

The results were forwarded to the Camden County Prosecutor's Office on Monday. They showed that Chevonne Thomas, 34, had smoked marijuana and phencyclidine, a hallucinogenic known to cause extreme violence in some users, said Jason Laughlin, spokesman for the prosecutor.

On Aug. 22, Thomas, who suffered from mental illness and twice lost custody of her son because of drug use, stabbed and cut the head off 2-year-old Zahree, put the head in a freezer, and then fatally stabbed herself in her Parkside apartment, police said.

Questions remain whether child welfare workers adequately monitored Thomas. They returned custody on April 3, finding she was fit to care for her son.

Thomas lost custody of her son in November 2010 and in July 2011 after smoking marijuana laced with PCP, once telling authorities she could not remember where she left her baby, records show.

Days after Zahree's death, state officials promised a thorough investigation.

Allison Blake, commissioner for the Department of Children and Families, did not return repeated calls seeking comment. In the past, the department had said Thomas received counseling, passed drug screens, and was visited by state workers.

The department did not specify how often state workers visited, how often she had been drug-tested, or whether an expedited investigation of Zahree's death had been completed.

State officials have not disclosed the treatment provided for Thomas' mental illness. Thomas, in a 911 call the night she killed her son, said she had a prescription for the antidepressant Prozac.

The department, citing confidentiality, has turned down requests by The Inquirer and a child advocacy group seeking documentation.

"There are still many unanswered questions, especially about visitation. How often did the mother and child visit prior to reunification?" asked Cecilia Zalkind, executive director for Advocates for Children of New Jersey.

Visitation is critical for very young children to determine whether a parent and child can be safely reunited, Zalkind said.

"It's not just getting the facts on this case. It's about getting information on how very young children are being protected in New Jersey," she said, noting that New Jersey lacks detailed reviews for child fatalities and needed reforms.

At the time Zahree was killed, the department released two press releases but did not respond to specific questions.

"It is our responsibility to initiate a thorough and comprehensive case review of our history with the Thomas family," said a statement released Aug. 24 by Kristine Brown, department spokeswoman.

"As is always our intention, we plan to provide you with as much information as possible within the confines of the law," the statement said.

No information has been released since Aug. 24, and Brown has not returned calls seeking further comment. Before Zahree died, state workers had been closing his case.

The department has been under the supervision of a federal judge since 2003 after high-profile lapses in oversight.

A federal monitoring report released in July documented that state workers' caseloads were increasing. It also noted that more than half of the children reunited with family did not receive visits twice a month as required.

New Jersey has a Child Fatality and Near Fatality Review Board independent of the Department of Children and Families. It provides impartial reviews of individual cases and recommends systemic improvements to protect children, said its chairman, Anthony D'Urso.

This month, the board will release findings based on its review of 2010 cases, which D'Urso said addressed monitoring. He would not disclose details.

Friends of Thomas said Monday that she had been receiving counseling and cared deeply for her son.

"She was a wonderful mother," said one friend, Lisandra Arroyo, who spoke to Thomas shortly before the deaths.

Another friend, Anthony Davis, described Thomas as a happy person. Both friends said that they believed Thomas appeared fine and that they were shocked by the deaths.

Davis said Thomas was working hard at counseling while caring for Zahree. He said, "I told her how happy I was for her and that I was proud of her."

Contact Barbara Boyer at 856-779-3838, bboyer@phillynews.com or on Twitter @BBBoyer.