A man, 18, has been arrested for allegedly sexually assaulting a woman on the same night and on the same tram line as the fatal attack on 21-year-old university student Aiia Maasarwe.

Investigators have been told a 20-year-old woman got off a route 86 tram on Plenty Road in Preston about 10.44pm on January 15.

Student Aiia Maasarwe was killed metres from a tram stop in Bundoora, in Melbourne's north. Credit:Instagram

Police say a man got off the tram at the same time and approached the woman on Bell Street, where he allegedly sexually assaulted her.

An 18-year-old Coburg man was arrested on Monday night, days after police released CCTV footage of a man on the tram that night.