Four daughters whose bodies were found in a Washington D.C. house with their mother died by homicide, but the coroner couldn't say how they were killed because their remains were so badly decomposed.

Toxicology results released Wednesday ruled out death by overdose of common prescription and over-the-counter medications for the daughters of Banita Jacks, according to the medical examiner's office.

But there's a chance the girls, ages 5 to 16, might have been poisoned, according to the coroner, who said not every toxic substance had been eliminated as a possible culprit.

Jacks, 33, has been jailed on murder charges since January. Detectives said she told them the girls were possessed by demons and died while they were sleeping. On Feb. 11, Jacks was ordered to remain in custody while a grand jury investigates; the next hearing is set for April.

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When the bodies were discovered Jan. 9, there was evidence that one girl had been stabbed. The others had markings on their necks and various signs of trauma.

But on Wednesday, the medical examiner's office said the remains were too decomposed to make a clear determination on what, if any, injuries caused the sisters' deaths.

Because of the inconclusive toxicology results, the manner of death has been listed for the four as homicide, but the cause reads "undetermined" on their autopsies, said D.C. Mayor Adrian M. Fenty.

A social worker believes Jacks had taken at least one of the sisters hostage in the home as early as April.

The case has drawn fire because the child welfare agency stopped its investigation based on a belief that the Jacks had relocated to Maryland — despite the fact that authorities couldn't find an address there for the family.

Fenty said his office is continuing its investigation into what role, if any, city welfare workers played in the tragedy.

“This, without any question, is one of the most — if not the most — heart-wrenching cases that’s ever happened in the District of Columbia.” the mayor said Wednesday after toxicology results were disclosed.

Police detective Mitchell A. Credle testified Feb. 11 that Jacks told investigators she did not want her oldest daughter to be a bad influence on her other children.

Credle said Jacks told investigators she had had two physical fights with Brittany Jacks and had called the girl "Jezebel." And she wanted to rid her daughters of the demons that possessed them, according to Credle.

The detective said Jacks' home was mostly empty, lacking food, clothing and furniture. Neighbors reported that Jacks and her children were seen in May removing furniture that Jacks said was covered with ants, he said.

Brittany dropped out of classes in early March. A social worker from the Booker T. Washington Public Charter School went to the home April 30 and called police after she was denied entry, Fenty said.

The social worker reported that after speaking to Jacks, she appeared to be mentally ill and "was possibly holding Brittany hostage by refusing to allow her to attend school," the mayor said last month.
A police officer who responded also was denied entry to the house, but Jacks told him she was home-schooling the children.

Social workers visited the home several more times in the following weeks, according to the mayor, but there was no answer when they knocked at the door. He said the case was closed May 16 because they believed the family had moved to Maryland after finding an address of a relative they believed she was living with.

By mid-June, however, Charles County officials claimed they weren't able to locate the family and "nothing (was) done to reopen the case," said D.C. Attorney General Peter Nickles.

The family did have relatives who live in Maryland, including Jessie Fogle, grandmother of two of the girls. She told The Associated Press that the family's living situation began to deteriorate in February after their father, Nathaniel Fogle Jr., died of cancer.

Jessie Fogle said she helped them rent an apartment, but they were later evicted and lived out of a van and hotels for several months before settling at the Washington address where the bodies were found.

The grandmother said she tried to see Jacks after her son's death, but no one answered the door and when she returned home, there was an abusive voice mail from Jacks berating her for visiting.

The grandmother said she made another attempt to contact Jacks a few months later, but again no one came to the door.

When she learned what happened to the children, "I just started screaming and hollering," she said. "It devastated me. I had been praying to God to bring them home to me."

The city's medical examiner has said the bodies were likely in the apartment for more than 15 days before their discovery. Jacks has told police that the deaths occurred before a utility turned off her electricity, which prosecutors said was in September 2007, according to charging documents.

FOX News' Catherine Donaldson-Evans and The Associated Press contributed to this report.