The 21-year-old was found naked in Kurilpa Park in South Brisbane last Friday morning with no possessions except for some jewellery.
Her clothes and bag have yet to be found and police divers are searching the nearby river.
Police said Ms Collombet was last seen leaving the Cultural Centre Bus Station at 8.47pm on Thursday March 27 and walking along the boardwalk adjacent to the Brisbane River in the vicinity of the Kurilpa Bridge.
They described the attack as “brutal” and said the cause of death was “brain injury by blunt trauma”.
The 21-year-old was last seen on CCTV wearing dark denim jeans, black boots, a beige singlet and a cream shoulder bag.
Those items are yet to be recovered and police urged anyone with information which could assist the investigation to contact Crime Stoppers anonymously on 1800 333 000 or crimestoppers.com.au.
Image via Queensland Police