"There are suspicions that things may not have been handled as they should," Adrian Fenty, Washington's Mayor admitted Friday, revealing the family had been struck off the social services list because they had no fixed abode.

The mother of the four girls, aged five to 17, had continued to live in the flat in a run-down area of Washington after they died.

The corpses were only discovered on Wednesday after police came to investigate.

The mother, Betina Jacks, 33, is in custody and risks life imprisonment if she is found guilty of charges of murder.

She acknowledged she had not fed her daughters for some time.

She told police: "They began dying in their sleep one at a time all within a seven to 10 day period."

Fenty said the girls had died after the electricity to their home was cut off, which according to records was in September. But an initial autopsy has placed their deaths at about two weeks ago.

The autopsy also showed that the oldest child had knife wounds in her stomach, while the three others died of suffocation or poisoning.

Inquiries have revealed that the Jacks family had been known to social services for some time.

In 2006 a doctor reported his concerns about the family and their living conditions but authorities "closed the case because they had no fixed address and lived out of a van," Fenty said.

The father at the time was alive but was suffering from leukemia, while the mother was a known drugs user.

Since March 2007, the girls had not been attending school with the mother saying she was schooling them herself at home, although no proper checks were carried out.

Police discovered the bodies as they were about to carry out an expulsion order, finding all four lined up on the floor of the bare apartment.