Robert Issa, 27, was gunned down at Craigieburn Central Shopping Centre in Melbourne's north in October 2023.
Four men wearing balaclavas surrounded Mr Issa's Mercedes SUV, firing multiple shots into the passenger side and rear windows.
He was killed and another man, a now 30-year-old from Hadfield, was taken to hospital in a serious condition.
A group of men, described by Victoria Police Detective Inspector Dean Thomas as alleged "foot soldiers", were arrested over the shooting last week but those police say ordered the hit remain at large.
"This reward today is very much focused at trying to identify those people further up the chain that were involved in arranging, organising and ordering the hit on Robert Issa," Det Insp told reporters at Victoria Police headquarters on Monday.
Police are keeping an open mind about whether criminals ordered the killing from Victoria, interstate or overseas.
Det Insp Thomas said there was no evidence it was linked to a long-running conflict over illegal tobacco profits or Kaz Hamad, who police allege is a Middle East-based crime boss.
"I'm confident there are people out there that know who has ordered the hit," he said.
"I am confident and I hope that this reward will be enough to prize them to come forward and share that information with us."
Five men were arrested in raids across Melbourne's north and east on Thursday and each charged with murder, attempted murder and criminal damage by fire.
Det Insp Thomas said he could not comment "one way or the other" on reports a sixth man was reportedly arrested in Greece over the killing.
A spokesperson for Attorney-General Michelle Rowland confirmed an individual was arrested in Greece on July 31 after an Interpol notice was issued on Australia's behalf, but did not provide details.
"As this matter is subject to proceedings in Greece, it is not appropriate to comment further," they said.
Police allege Mr Issa had connections to several organised crime groups.
The Director of Public Prosecutions will consider granting indemnity from prosecution to anyone who provides information on the identity of the main offender or offenders.
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