THEY believe Elias Herodotou, 28, from Coburg, may have information that could solve the murder of Thornbury man Darren John Webb, 40.
Mr Webb died of a cut to the neck in an eighth floor room of the Crown Metropol early on Sunday morning.
Detective acting Senior Sergeant Mark Hatt wouldn't reveal what role Herodotou may have played in Webb's death, but they think he might have been there on Saturday night.
"We believe he was present at the hotel on the evening of the incident, and we would hope that he would come and speak to us about that," the detective said.
"Investigators have been speaking to members of his family and we have been trying to negotiate with him to come forward and at this stage we would appeal for him to do that."
Both men were known to each other, and to police, though Detective Senior Sergeant Hatt would not reveal how.
Members of the public are urged not to approach Herodotou, and to call 000 if they know his whereabouts.
Police have previously said that at least two other people may have been inside the hotel room when Webb was killed.
There are unconfirmed reports Herodotou and Webb may have become involved in a fight over a girl, or room service charged to a credit card.
It is also believed Herodotou may have contacted a lawyer on Sunday night.
A Crown employee says staff have heard unconfirmed reports that Webb was found with multiple syringe stab wounds to his neck.
Crown Casino says it cannot comment while a police investigation is underway.