A woman believed to be in her 20s has been found dead in a serviced apartment at Oaks on Market in Melbourne's CBD, where a group of men from Canberra were reportedly celebrating a buck's night.
Four men, all aged in their late 20s to early 30s from the ACT and NSW, are now in custody assisting with the investigation.
The woman's death is being treated as suspicious, but exact circumstances remain unknown, police said.
Police were trying to establish whether the woman had been known to the men, and if she had consumed drugs and alcohol.
The men, all aged in their late 20s and early 30s, had travelled to Melbourne from the ACT and NSW for the party.
Two of the men told Fairfax they went out to a football match before hitting the town.
Seven of the men, who have been described as witnesses to the incident, left the hotel about 2.30pm.
They would not say how they met the woman or who she was.
It appears that the group of men were not the ones who called emergency services.
Police refused to confirm the woman's identity on Monday, despite ruling out foul play.
Anyone with information can contact Crime Stoppers on 1800 333 000.