The parents of a 3-year-old Arizona girl who weighed just 15 pounds when she died have pleaded not guilty to murder and child abuse charges in a case that has renewed scrutiny of Arizona's child protection system.

Thirty-six-year-old Rosemary Velazco and 28-year-old Carlos Cruz entered their pleas Thursday in Maricopa County Superior Court in Phoenix.

Their nearly 4-year-old daughter was found dead May 23. A relative had called police to the couple's home because the girl was unresponsive.

Police said the girl showed signs of extreme malnourishment and had injuries that included a cut exposing her skull.

She'd been placed in foster care at birth because she tested positive for methamphetamines but was returned to her parents after they completed substance abuse and parenting classes.