A Phoenix man is charged with first-degree murder after police say he beat his girlfriend's 3-year-old daughter to death over the weekend.

In addition to blunt force trauma to the girl's head and torso, police also noticed bite marks on the young girl, which were admittedly caused by her mother's unemployed, live-in boyfriend, 18-year-old Martwane Mackey.

Mackey called police about 2 p.m. from a payphone down the street from the apartment he shared with the girl's mother at 1601 West Missouri Avenue in Phoenix.

When police arrived at the payphone, they found Mackey holding the toddler. She wasn't breathing.

Rescue crews tried to revive the girl, but were unsuccessful and she died.

Because his girlfriend works, and he doesn't, Mackey was tasked with watching the girl and her 1-year-old sister that morning.

According to court documents obtained by New Times, Mackey admitted to abusing the girl -- and her 1-year-old sister, who was found to have similar injuries but is expected to survive.

Mackey told police that earlier in the day, the 3-year-old had a "choking incident" that left her unconscious and not breathing at times. Rather than call 9-1-1, Mackey thought biting the girl on the face and torso might bring her back to consciousness, he later told police.

Mackey had no explanation for the bite marks on the girl's younger sister, though.

Mackey admits to abusing the girl, but claims he didn't kill her. He told police he suspected she may have hit her head on the toilet, or something, but maintains that he didn't cause her death.

In addition to the murder charge, Mackey also is charged with two counts of child abuse. He was booked into a Maricopa County Jail on $1 million bond.

• Crime