Nathalyz Rivera, a little girl with special needs, suffered and starved to death in a filthy rowhouse in Philadelphia's West Oak Lane section, police say.

She was already dead when her mother brought her, wrapped in a dirty blanket, to Einstein Medical Center early Monday, authorities say. She was almost 4 years old - and weighed 11 pounds. She weighed the same as an average 3-month-old. Her bones were visible through her skin, authorities said. At the hospital, a roach scurried across her body.

"This is one of the worst cases of abuse that I've seen in my five years on the homicide unit," Capt. James Clark said during a news conference Monday announcing that the medical examiner had ruled the child's death a homicide by starvation.

Late Monday night, Nathalyz's parents - Carmen Ramirez, 27, and Carlos Rivera, 30 - were charged with murder by the Homicide's Special Investigations Unit.

Earlier Monday, police had been trying to determine who had been the child's primary caretaker at the Sommers Street house where Nathalyz lived with her parents and siblings - and how long the girl had been starved.

Ramirez told investigators that Nathalyz was born blind and with Down syndrome.

The couple's other children - Nathalyz's twin brother and three other siblings, ranging in age from about 5 to 9 - were placed in the custody of the Department of Human Services and were being examined by doctors. They were said also to have suffered from insect or rodent bites.

Their sister's condition suggested she had "starved like people in concentration camps starved," said Cindy Christian, a child-abuse pediatrician at Children's Hospital of Philadelphia who is medical director for the Department of Human Services.

Christian said she had not yet reviewed Nathalyz's previous medical records - if any exist - but said it was clear from the facts that had come to light that she had long suffered.

"This doesn't happen to a child in a couple of weeks," Christian said. "Generally, it is a process that takes months and months, or even years of neglect."

The family had one previous contact with DHS, Clark said, but he had no details. Sources said a complaint was made against the family around 2008, before Nathalyz was born.

Alicia Taylor, a DHS spokeswoman, said confidentiality laws prohibited her discussing the family.

"We are working with police," Taylor said. "Our job is to make sure that the other children in this family are safe, and that includes that they are checked out of the hospital and cleared medically."

Clark, of the homicide unit, said the photos of the girl's body were "extremely disturbing." He said the child had festering wounds, likely caused by insects or rodents.

The house where she lived was flea-infested, he said. Crime scene investigators in protective hazmat suits searched the house Monday night.

Clark said police initially put together this timeline: Around midnight Monday, the girl's father, Rivera, discovered that she was not breathing.

At the time, the girl's mother, Ramirez, was at a boyfriend's house, police sources said. Instead of calling 911, they said, Rivera called Ramirez.

The mother and her friend picked up Nathalyz and took her to Einstein. The girl was pronounced dead at 1:50 a.m. It is believed she may have been dead for hours.

Ramirez lived at the home, but in the last three weeks had been spending some time at the boyfriend's house, police sources said. But "she saw this child's condition during her time at home," Clark said.

After Ramirez was arrested at the hospital, the father dropped off the other children at a friend's house Monday afternoon and then fled, Clark said. The father was arrested hours later.

Court records show Rivera had had arrests on drug and assault complaints in Philadelphia and Delaware, and twice served jail terms on drug charges.

Neighbors on Sommer Street said the couple moved in about four years ago and kept mostly to themselves, using the rear-alley entrance and angering some on the well-kept street by letting their grass grow tall. Trash litters the rotting back roof and the overgrown backyard. Princess curtains adorn an upstairs window.

Annetta Dangerfield, who lives next door, said the couple fought just weeks after they moved in, with Rivera breaking out all the front windows.

"I called the owner immediately and said, 'We don't have this in this neighborhood,' she said.

The parents rarely let the children out front to play, Dangerfield said. Ramirez told her Nathalyz couldn't see, talk, or walk - and "was born that way," Dangerfield, 82, said.

Ramirez would carry the girl to the car in a car seat, the neighbor said.

The older children looked thin, she said, and were not always clean. "But they were beautiful children," she said.

The couple rented, she said, and Rivera sometimes fixed neighbors' cars for cash. Ramirez also worked, she said.

In April, Dangerfield said, one of the couple's pit bulls bit her leg. The couple agreed to pay her $65 medical bill, she said.

Dangerfield said that on Saturday night, she heard crying through the wall.

"The baby cried for about an hour and a half," she said. "Just cried constantly."