Moala Sia Foʻou Tātola, 40, and Tāfolosa Haisaane Tātola Mahe, 47, accused of negligently killing their mother after her decaying body was found lying in filth in their home two years ago,pleaded not guilty in a San Mateo court last Friday

According to US media prosecutors filed charges against the sisters after concluding they criminally neglected their 73-year-old mother while they lived together for about two years, San Mateo County District Attorney Steve Wagstaffe said Monday.

The siblings were living with their mother as caregivers in a home in the 1600 block of East Third Avenue in San Mateo from sometime in 2011 until her death in early 2013, prosecutors were quoted by US media as saying.

They reported their mother’s death on March 9, 2013, and when police arrived, they found the mother lying nude on the bed, already decaying with faeces all around her. Her back and legs were nearly black from filth, gangrene and dying flesh, prosecutors said.

An autopsy revealed the woman died of pneumonia. The sisters told investigators they tried to care for her but she refused to go to a doctor despite suffering from diabetes. However, they said they didn’t notice the squalid condition she was in before her death, prosecutors said.

Wagstaffe said that after a lengthy investigation and review process, it was clear the woman could not have ended up in the condition she did if the daughters were not criminally neglectful.

For example, if she refused to go to the doctor, the sisters could have sought assistance from San Mateo County Adult and Aging Services, he said.

While the pathologist was unable to pinpoint exactly when the woman died, it’s possible the sisters continued living with her for some time before reporting her death, Wagstaffe said.

The woman “couldn’t be in that condition without being totally ignored,” Wagstaffe said.

The sisters remain in custody on $150,000 bail and are scheduled to return to court for a preliminary hearing on Nov. 25.