They escaped uninjured after two bullets went straight through the building.
The drive-by has prompted force command to review security at the 24-hour facility that houses cars seized by police.
One particular car may be of interest to detectives.
Fairfax Media was told a car belonging to a member of the Hells Angels motorcycle gang was seized just hours before.
It is understood the Echo taskforce – which investigates outlaw motorcycle gangs – is now assisting with the investigation into the shooting.
But police would not comment on whether the impoundment related to the shooting.
Darebin crime investigation unit Detective Senior Constable David Hatherly said earlier the actions of those involved were callous.
“The behaviour displayed by the people who have done this is heinous, it’s a low act and it’s putting people’s lives in danger,” he said.
He said the investigation was still in its infancy so there was not yet a solid line of inquiry.
One passer-by had come forward to help police, but there were other witnesses in the area that police want to speak with.
Senior DetectiveHatherly said investigators were reviewing CCTV footage in the area.
Police have not yet determined the type of firearm used.