Six years, six spree killers, 35 homicides.Australia, like many countries, doesn't list a death as being a homicide until someone is convicted of the killing.
Australia's National Homicide Monitoring Program, administered by the Australian Institute of Criminology, tacks homicides in Australia. The Australian Institute of Criminology is Australia's national research and knowledge center on crime and justice.
The National Homicide Monitoring Program has this to say about the definition of 'homicide':
Homicide is defined by the criminal law of each Australian state and territory. As a result, varying definitions exist between states and territories in terms of its degree, culpability and intent.
Since there is no national definition of exactly what constitutes a 'homicide', the NHMP uses the following definition(my comments in blue follow each point):
* all cases resulting in a person or persons being charged with murder or manslaughter.
In order for a killing to be classed as a homicide under this criteria, a person must be charged with the crime. No suspect in custody or no charges filed, no homicide.
* all murder–suicides classed as murder by police
Remember that each state and territory is left to define murder and homicide. If the police in a particular jurisdiction don't declare it to be a murder, it is not a homicide. Likewise, for the police to declare it to be a murder, there must be a dead suspect for it to be a murder/suicide. If there is suspect dead from suicide, there is no homicide.
This is an important distinction. The shooter in the Sydney Hostage incident of 2014 was not listed as a homicide incident, despite the fact that the shooter killed two people. Why? Because he was killed by the police. The killings were listed as terrorism, despite evidence that the shooter was a serial rapist, and was out on bail after being charged with the murder of his wife.
* all other deaths classed by police as homicides
Again, the laws vary between each territory and state. What one police department classifies as a murder, another may not. This makes it nearly impossible to determine the number of homicides.
The real problem with using ANY data from other countries as a yardstick to measure the effectiveness of restriction on firearms ownership is that different countries use different methods and definitions, making a direct comparison of data useless for statistical and comparison purposes.