This joint Four Corners/Fairfax report from 2015 revealed damning evidence that the investigations of key gangland murders in Victoria were deeply flawed, undermining the criminal justice system in the state.

Terry Hodson and Carl Williams were career criminals. Hodson was shot twice in the head by a killer who'd come to his home with no apparent sign of a break-in. Williams was bludgeoned to death while in jail.

Two murders - six years apart, both linked by key facts. Each was a police informant; both had made serious allegations of police corruption; both were killed with police acutely aware both men were in danger.

Despite the extraordinary circumstances of the deaths, it's still not clear who ordered their killing. To this day, no one has been convicted of the murder of Terrence Hodson and his wife Christine.