The body of Aiia Maasarwe, 21, was found near La Trobe University in the city's north. She had taken a tram home late on Wednesday after a comedy show.
Her sister "heard the sound of the phone falling to the ground and heard some voices", officer Andrew Stamper said.
Police are searching for the killer.
They have not ruled out the possibility that Ms Maasarwe was sexually assaulted, Melbourne's Age newspaper says, with known sex offenders "an active line of inquiry".