Four Philadelphia social workers charged with fraud in a case linked to the starvation death of a disabled teenager defended their work as their trial opened Wednesday, saying they were not paid for any medical expertise.

In an unusual criminal case, federal prosecutors are trying to prove the social workers defrauded the city of millions of dollars aimed at helping the neediest families on city welfare rolls.

Danieal Kelly's family fit that description. Her unfit mother was raising six or seven children alone in a squalid two-bedroom rowhome.

Danieal, who had cerebral palsy and could not walk, had once thrived in the care of her father and stepfather in another state. But before she died in the stifling apartment in August 2006, the 14-year-old was spending most of her time in bed, without much schooling, medical care or even sufficient food and water. She weighed just 42 pounds, and had severe, maggot-infested bedsores.

Andrea Kelly is serving 20 to 40 years in prison after pleading guilty to third-degree murder in state court.

The federal defendants include the founders and supervisors of MultiEthnic Behavioral Health Inc., which was paid $1 million a year to oversee a relatively small caseload of high-risk families.

Federal prosecutors charge that they huddled in the hours after Kelly's death and created documents to purport they had made the required twice-weekly visits to the Kelly home and others.

"This is a case about protecting children," Assistant U.S. Attorney Vineet Gauri said in opening statements. "It's about a company that said, 'Pay us, we'll be that safety net. We'll make sure these kids are safe."'

Defense lawyers emphasized that their clients are social workers, not doctors — and that many others also missed Danieal's deteriorating condition, which they said Andrea Kelly worked hard to conceal. Two school employees visited about six weeks before she died to assess her educational needs.

"They left without blowing any whistles. They didn't find that there was anything wrong with little Danieal," said William Cannon, who represents company founder Mickal Kamuvaka.

Kamuvaka holds a doctorate in social work from the University of Pennsylvania. Defense lawyers described their clients as hard workers who chose a profession where they could help others.

Kamuvaka and co-defendant Solomon Manamela founded the company in about 2000 to bid on the city contract. The other defendants are Kelly family caseworker Julius Juma Murray and social worker Mariam Coulibaly.

Kelly's father, Daniel, remains charged in state court with child endangerment, for allegedly abandoning his daughter at Andrea Kelly's chaotic home.

The social workers are charged with fraud and conspiracy, not murder. But the harrowing photos of Kelly's emaciated, dehydrated body will hard to forget during the monthlong trial, Coulibaly's lawyer conceded.

"Danieal Kelly is the elephant in the room in this case," lawyer William Brennan told jurors. "There's no getting around it."