NEW YORK - (AP) - Three years before 4-year-old Marchella Piercewas found starved, beaten and drugged, the city's own investigatorssaid child-welfare workers had failed to protect the vulnerable.

New York City's child-welfare agency had overseen 11 cases inless than a year in which a child died after workers reported thechild was living in a safe, clean home. In all but one, the 2007investigation charged, the Administration for Children's Servicesdid inadequate or incomplete work. The inquiry prompted majorreforms, but no caseworkers were held criminally responsible.

New York prosecutors now say the reforms might not have worked.They took the rare step of charging two child welfare workers withhomicide, saying their job failures - and efforts to conceal them -cost Marchella her life.

Brooklyn District Attorney Charles Hynes said Wednesday thatthe negligence of caseworker Damon Adams and supervisor ChereeceBell went beyond poor job performance: They are accused ofdoctoring reports to show more visits to Marchella's home than weremade. They pleaded not guilty.

Marchella's mother was on ACS' radar after she gave birth to ababy boy who tested positive for drugs. The 4-year-old had beenborn premature with underdeveloped lungs. She had a breathing tubein her throat and spent much of her life hospitalized.

She was allowed home in February 2010 and was dead seven monthslater from battered child syndrome, Hynes said. Her mother has beencharged with murder and grandmother with manslaughter; they havepleaded not guilty.

Adams was accused of adding at least five phony reports thatsaid he had visited the home. Prosecutors say he couldn't havevisited because if he had, he would have seen Marchella's veryvisible injuries.

In an eight-month stretch starting in October 2005, 11 childrenwho had been under ACS' care died; another nearly drowned.

In the most notorious case, 7-year-old Nixzmary Brown wasstarved and beaten to death by her stepfather in 2006. Nixzmary'smother is serving a prison sentence of up to 43 years for failingto help her battered, malnourished child. Her stepfather is serving29 years on a manslaughter conviction for delivering the fatalblow.

The investigation by the city Department of Investigationoutlined a troubling pattern of lying, incompetence, carelessnessand ill-trained caseworkers. It gave grim details about thechildren, whose deaths likely could have been prevented.

The department made a list of serious recommendations. Many wereimplemented, including hiring additional caseworkers, an increasein coordination with other city agencies and a new case-trackingsystem.

Since then, there have been more than 300 layoffs in other areasof the agency, and the city's contribution to its budget hasfaltered.

Hynes has ordered a special grand jury to consider evidence ofsystemic failure and determine whether the investigators'recommendations were followed.

Mayor Michael Bloomberg said Thursday that they generally were.

"Whether they are followed in this case ... it's aninvestigation, and I just can't answer," he said, expressing "100percent confidence" in longtime ACS head John Mattingly.

The results of the charges in Marchella's case have beenprofound for ACS workers, said Faye Moore, the spokeswoman fortheir union. On a visit Thursday to the unit where the two worked,people were panicked and tearful, she said.

"This was a structural failure, a system failure, thanks tobudget cuts, and other reductions in the agency," she said. "Theyare not responsible for that, and they are being housed withcriminals. It isn't right."

The accused workers are being held on bail. They are inprotective custody because, their lawyers argued, they are nowbeing jailed with people they previously investigated.

City spent $11 million on provider for dead girl Death of BK girl, 4, prompts grand jury review DA opens criminal probe in death of 4-year-old 2 ACS workers suspended following 4-year-old's death