$100k reward for Melb attempted murder

A Melbourne gym owner who is lucky to be alive after bullets were fired across his face still wonders why someone tried to kill him.

Police say only "sheer luck and the grace of God" prevented Nicholas Solomos from being at least seriously injured when a masked gunman attempted to murder him by firing three shots though his car window in May last year.

No threats were made before or after the shooting in Mockridge Avenue, Burnside, Mr Solomos says.

He admits it is "a bit daunting" knowing the shooter is still on the run.

"You're always watching your back because the unknown and the why is always a question mark on my head," he said on Wednesday.

The gunman said nothing during the attack before running to a waiting vehicle.

Police speculate Mr Solomos' expanding gym business may be a motive but cannot be sure and have offered a $100,000 reward for more information.

Four people were interviewed on Tuesday and have been released, police said.

Mr Solomos needed treatment for cuts from the shattered glass after the attack that police believe was an attempted murder.

"If you fire three shots into a driver side window, there is every likelihood that the person will at the very least be serious injured," Detective Inspector Stephen Clark told reporters.

Police released a digital image of a person, who may not be the gunman, who they suspect can help the investigation.