PHOENIX -- A Phoenix man has pleaded guilty to second-degree murder and child abuse stemming from the death of his girlfriend's 3-year-old daughter.
Martwane Mackey entered his pleas in Maricopa County Superior Court on Friday.
Phoenix police say that Mackey called 911 around 2 a.m. on June 25, 2011 and said that Tyshea Austin wasn't breathing.
When police arrived, they saw bite marks and injuries to her head and torso, and said that she appeared to have been dead for some time.
Investigators found similar injuries to her 1-year-old sister.
Police said that Mackey, 18 at the time of the crimes, admitted to abusing the girls but denied causing Tyshea's death. He will be sentenced in January.