Officers were called to an apartment near Broadway Road and Dobson, early Friday morning for a report of a child not breathing.
A young girl was found unresponsive inside the home and paramedics rushed the child to the hospital.
Despite life-saving efforts, the girl was pronounced dead at the hospital.
Authorities say there were clear and obvious signs of trauma to the child.
Through the investigation officers learned that the child was in the care of a step-father when the injury occurred.
Police detained and questioned 27-year-old Andrew Isaacs. He told detectives the children were playing and the young girl fell and hit her head.
"He alleges that the child fell and hit her head, and then later on during the interview he admits to possibly rough housing with the child and perhaps being too rough," said Steve Berry with the Mesa Police Department.
Isaacs was arrested and charged with one count of child abuse.
Friends say they can't believe what happened.
"That is really sad, I mean I did see him spank her, but I was spanked when I was raised, so I didn't think anything of it," said a friend.
The Department of Child Safety released a statement Friday stating that a DCS specialist was assigned to investigate a December 2014 report that Isaacs was abusing the child. The specialist made only one attempt to contact the family, but did not follow up.
Director Greg McKay stated, "When allegations of abuse or neglect are made, the Department of Child Safety has a responsibility to confirm that children are safe. We are fully committed to conducting an in depth review of cases that result in tragic outcomes and what, if any, part we played. This is yet another dreadful reminder of the violence people are capable of and the devastating consequence on our most vulnerable citizens."