FREDERICK, Colo.  — The bodies of two young girls were submerged in crude oil for four days before authorities discovered them, according to court documents filed by an attorney defending the girls’ father against accusations that he killed his children and wife.

The motion filed Friday by Christopher Watts’ attorney, James Merson, also asked that DNA swabs be taken from the girls’ necks. The request quotes an expert who believes the oil would not eliminate DNA and said samples can be obtained “after strangulation.”

Authorities separately announced that the Weld County Coroner’s Office had performed autopsies on Friday and confirmed the bodies as 34-year-old Shanann, 4-year-old Bella and 3-year-old Celeste Watts.

Police did not release any information about how the mother and daughters died. More testing is planned to help determine the cause of their deaths.

Richard Eikelenboom, the expert cited by Watts’ attorney, also recommended taking DNA samples from the girls’ hands and the hands and nails of their mother.