A police helicopter circled the area after police and paramedics attended the scene.
A video seen by The Age showed Maghnie and one other man lying on the ground, topless, being attended to by paramedics.
Underworld sources described Maghnie as a “dead man walking” amid his increasingly aggressive behaviour towards rivals in bikie groups and other organised criminal syndicates.
Maghnie, 44, was known as a habitually violent criminal, with a notoriously hair-trigger temper and a penchant for waging private vendettas publicly.
“It was only a matter of time,” one criminal source said. “You can’t do what he did without pissing off a lot of people – people won’t stand for it.”
Maghnie is also a suspect in the attempted murder of Bandido Toby Mitchell in 2011.
In a statement, police said homicide squad detectives would lead the investigation.
“The exact circumstances surrounding the shooting are still to be determined and the investigation is ongoing,” the statement read.
Anyone who witnessed the incident or who has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au