Police in Melbourne are questioning a man about the killing of a leading underworld figure.
Macchour Chaouk, 65, was shot dead in his backyard at about 11am on Friday.
Detective Superintendant Murray Fraser says officers are on standby for a possible revenge attack from another family that has a long-running feud with the Chaouks.
The ABC reports police and the family's own lawyer Alan Swanwick have told the courts on a number of occasions the two families are "at war".
Two other men were shot dead at a bar in Melbourne on Friday afternoon. A third man escaped and another is being questioned.
But police say there appears to be no link with the earlier shooting.