The girl had gone missing on Monday and her body was recovered yesterday from the Jalalabad area in Nazimabad.
"The autopsy reports have confirmed she was sodomised and strangled to death," Additional Police Surgeon Dr Rohina Hasan said.
"I have never seen such brutality inflicted on an infant in my career," she said, adding the autopsy report also confirmed torture marks on her body.
Senor police official, Munir Sheikh said the police had obtained some clues and would arrest the killer within next 24 hours.
He said the family members of the girl had reported that her body was found in a street outside her home.
Further investigation into the matter is under way, with authorities launching a massive manhunt to nab the perpetrator.
