Casey Crime Investigation Unit detectives are investigating the circumstances surrounding two incidents at a shopping centre in Narre Warren on 15 October.
Police were called to a report of a robbery near the bus terminals at the centre on Overland Drive just after 6pm.
It is believed a male was approached by unknown offenders who assaulted him and stole jewellery.
Whilst police were at the shopping centre, it is understood an incident on the rooftop carpark of the shopping centre occurred.
It is believed a group of unknown offenders, one armed with a baton, were involved in an assault about 6.30pm.
Police were not aware of the second incident until 17 October and no formal report has been made.
At this stage, no arrests have been made and the investigation remains ongoing.
It is believed the incidents are linked.
Any witnesses or anyone with information is urged to contact Crime Stoppers on 1800 333 000.
