A red plastic fuel container may help identify who shot a policeman amid a wave of violence that appears to have targeted the father and ex-wife of gangland killer Carl Williams.
Detectives say the container was left outside an Essendon house that was hit by up to nine petrol bombs early on Sunday morning.
The house is in the street where Ms Williams lived before reportedly moving out this week.
Police have described the attack as a possible case of mistaken identity.
Someone shot at George Williams’ Broadmeadows home early on Tuesday minutes before 31-year-old First Constable Ben Ashmole was blasted with a shotgun from another car during a routine traffic stop.
He suffered pellet wounds to the back of his head and was released from hospital on Wednesday after surgery.
Detective Inspector Steve Clark says police are investigating whether the shootings are linked to petrol bomb attacks at the Essendon house and a house in Mr Williams’ street.
“We’ve had some arson attacks where Molotov cocktails, for want of a better word, have been thrown at residences in those streets,” Det Insp Clark told reporters on Thursday.
“We’re exploring links between those attacks and the shooting of a policeman on Tuesday morning.”
Police have released an image of a red Scepter five-litre fuel container and a black Ford Escape SUV similar to the one used by the gunman and accomplice when Const Ashmole was shot.
A burned-out Ford Escape was found in an industrial estate in Coburg North soon after Tuesday’s shooting.
Police searched that area on Thursday for the shotgun used in the Moonee Ponds shooting of the officer.
Det Insp Clark asked petrol station owners to look through CCTV for sales of the petrol container, and for anyone on the Coburn North area with CCTV to review their footage.
He said Mr and Ms Williams were willingly helping police.
“We’re getting a whole lot of co-operation, so I’ve got no concerns there,” he said.
But he would not be drawn on whether the shootings and firebomb attacks were part of a wider conflict within Melbourne’s underworld.
Carl Williams was convicted of four murders during Melbourne’s bloody gangland war and was himself murdered in his Barwon Prison cell in 2010.