Four of five family members killed in a suburban Philadelphia apartment earlier this year were suffocated and the fifth was strangled, officials said Friday.

It's the latest development since authorities charged a mother and her adult daughter with killing their close family members in February.

Police say 46-year-old Shana Decree and her daughter, 19-year-old Dominique Decree, each face five counts of homicide and one count each of conspiracy.

The Bucks County coroner's office said Friday that Shana Decree's son, 13-year-old Damon Decree Jr., and daughter, 25-year-old Naa'Irah Smith, were asphyxiated. The coroner said Shana Decree's sister, 42-year-old Jamilla Campbell, was strangled, while Campbell's twin daughters, 9-year-olds Erika and Imani Allen were also asphyxiated.

The deaths were ruled to be homicides.

The coroner did not release any other details in the case.

Authorities haven't released a motive in the slayings and say the investigation is continuing.

The Decrees' attorneys declined comment.

The family members' bodies were found Feb. 25 in an apartment in suburban Philadelphia after Bucks County child welfare officials showed up unannounced and got no response when they knocked on the door.

A maintenance worker opened the door and found Shana Decree and Dominique Decree in a "disoriented" state, according to court documents.

Police arrived and found all five bodies in a bedroom. The apartment was in "disarray," with broken drywall and broken glass, overturned furniture, and other clutter.

Preliminary hearings in the case are set for later next month.