The common populist phrase ‘if you do the crime, you should do the time’ suggests that those who commit criminal offences should be caught and prosecuted – regardless of how trivial or outdated the offence may be, or how futile or costly it is to put this ‘zero tolerance’ approach into practice.

An example of an offence which many consider unjustifiably costly and futile to prosecute is the crime of drug possession – whereby ‘zero tolerance’ policing has done nothing to deter would-be offenders, has cost billions of dollars to enforce, and has led to a range of other socially undesirable consequences, including the stigmatisation of drug users, the reluctance of those whose use detrimentally affects their lives to seek medical help and a thriving black market with all the associated violence and health risks – including the dangers of low-grade drugs that contain potentially deadly fillers.

But what are the most frequently detected crimes in Australia?

And which offences tend to go unreported and undetected?

The most frequently detected offences

National statistics suggest that the most frequently detected offence-types in the year 2016/17 were:

Drug offences – 81,160 Acts intended to cause injury – 78,421 Theft – 78,093 Public order offences – 61,198

This does not necessarily mean that these are the most common offences committed, just that they are the most frequently detected. In fact, there is research to suggest that certain driving offences such as drink driving or negligent driving (eg failing to keep a proper lookout for pedestrians or other motorists) may be more common that all of those above, but they are less likely to be detected.

A factor in detection rates is also that many assault offences – which come under acts intended to cause injury – are committed in view of the public; a situation where police are most likely to be called.

A factor relating to the detection of drug offences is the pro-active detection policy of police; which is signified by the heavy presence of police and drug detection dogs at music festivals and other venues.

So as statistics can be skewed by a range of factors, the statistics on detection should not be equated with prevalence of offending.

Hidden crimes

Many types of crime go unreported to police which makes it difficult to estimate their prevalence or to identify perpetrators.

There are many reasons why someone may not want to report a crime to police including a belief that they won’t be taken seriously, a reluctance to dob in a friend or relative or concerns about re-victimisation either by the criminal justice system itself.

Victimisation surveys attempt to bridge the gap between reported crime and the actual rate in the community. These surveys find that the rate under-reporting depends a lot of the type of crime committed.

Whilst 90% of motor vehicle thefts are reported to police, only 39% of sexual assaults are reported.

Under-reporting of sexual assault has been well documented globally. The reasons for under-reporting differ between surveys but include wishing to deal with matters privately, feelings of shame and embarrassment and fear of not being believed by police.

Some advocates point to low rates of convictions as being a cause of reluctance by sexual assault victims. In Australia, only 1 in 6 reports to police of rape and less than 1 in 7 reports of incest or sexual penetration of a child result in prosecution.

Other offences with low detection rates

Physical assaults have notably low reporting rates, with only about half of such incidents being reported to police, usually because the victims view the crime as trivial or not worth reporting.

Domestic violence is noted as being one of the most underreported categories of crime globally. Domestic violence under-reporting is driven by a number of complex factors from financial or familial dependence to normalisation of violence and self-blaming.

Moreover, vulnerable communities such as Aboriginal and Torres Strait Islander people, as well as sex workers, are known to under report crimes due to a general distrust of police and the criminal justice system.

Unsolved crimes

Even when crimes are detected by, or reported to police, identifying offenders can be difficult if certain barriers to investigation exist.

There are no independent national statistics on the number of unsolved crimes in Australia. But, generally, the data indicates that a large number of reported crimes go unsolved, particularly property crime and theft.

A lack of (cooperative) eye-witnesses or CCTV footage of a crime, very little physical evidence and little connection between perpetrator and victim are all common factors likely to mean a crime goes unsolved.

An analysis of ‘solvability factors’ for homicide in Australia undertaken in 2001 found that unsolved homicides were more likely to involve a single victim, to have involved the use of a firearm and to have occurred in a non-residential area.

Police factors in unsolved homicides included failures by police to rapidly secure a crime scene and a lack ample resources devoted to the investigation.

Generally, crimes committed between strangers are difficult to solve, particularly if there is no clear motive that can narrow down potential suspects.

Finally, perpetrators that have no prior criminal record are less likely to come to the attention of investigators making it less likely for them to be identified.

So, not all crimes are equal when it comes to being caught.