The deceased men have been identified as 22-year-old Naresh Bhawanie, and 26-year-old Sterling Joseph.
Both men were gunned down at the Agua Splash Car Wash along Penco Lands, Longdenville, around midday on Thursday.
They were shot several times in the head and upper body.
Several spent shells - believed to be from a semi-automatic weapon - were recovered from the scene.
Police have no motive for the killing, however, they are working under several theories, the main one being that two were killed for failing to pay "protection money" to gangs in the area.
Investigators are expected to also return to the scene of the shooting on Friday.