The girl's mother, 23-year-old Sara Krueger and her boyfriend, 26-year-old Ryan Scott Warner, are charged with murder and felony assault on a child causing death.
Prosecutors tell ABC7 San Francisco they are waiting for autopsy results to tell them if there is evidence of sexual assault. If so, the suspects could face the death penalty.
ABC7 spoke with a member of the Slusher family Tuesday morning who said Kayleigh's death is the most horrible thing that could ever have happened. They have not yet decided on the funeral arrangements.
Kayleigh was found dead in her mother's apartment Saturday afternoon during a welfare check. Krueger and Warner were arrested Sunday.
Get more on this story from our sister station, KGO-TV.