Premier Barry O'Farrell announced at the weekend that this week the government will introduce a bill to make life sentences mandatory for people who murder police officers.

At the moment the minimum non-parole period is effectively 25 years.

With all due respect to police, who do an important and sometimes brave job, it seems odd that their lives should be valued so much more highly than those of the rest of us.

Imagine a scenario where someone is being robbed at knifepoint and a police officer, trained, equipped and paid to prevent crime, intervenes and is stabbed to death. Now imagine the same scenario where a member of the public intervenes and meets the same fate. Why should their death be punished less severely? In each case there has been a tragedy and a death, as well as a great loss to family, friends and the community.

One argument in favour of the new bill is that police officers represent the rest of us, and therefore an attack on one of them is an attack on the security of the whole society and deserves to be punished more severely. It is also the case that murders of police usually occur when they're trying to stop a crime, whereas murders of other people (despite my hypothetical above) usually occur in other circumstances. And murders of people trying to prevent a crime arguably deserve a higher punishment than those that occur for many other reasons.

I accept that argument. What I have difficulty with is the assumption that the punishment ought to be so much more extreme.

According to the Judicial Commission of New South Wales, the Crimes (Sentencing Procedure) Amendment (Standard Minimum Sentencing) Act 2002 (NSW) introduced the concept of the standard minimum non-parole period for certain specified offences. Murder now carries two standard non-parole periods: 20 and 25 years imprisonment.
"The higher non-parole period," says the Commission, "applies to cases of murder where the victim is a public figure exercising public or community functions and the offence has arisen because of the victim's occupation."

In other words, people who kill an on-duty police officer at the moment all else being equal will serve five years more than if they'd killed someone else. I'd suggest that's about right. But what is being proposed would probably double the time served by a 25-year-old person who killed a police officer, assuming they lived for 75 years. To me that seems disproportionate.

Why is the government introducing this law, which it has promised since 2002? The only reason given in the press release on the weekend was that Police Minister Mike Gallacher "said life sentences for those who murder police officers sends a very clear message that the community will not tolerate attacks on police officers''.

Presumably no one thinks the community tolerates the murder of police, and what the minister really means is that the new law will have a greater deterrent effect than the old one. If this were so, it would be hard to argue with the new bill. Unfortunately, though, American studies show little evidence that life sentences deter people from killing police officers (or anyone else).

Dr Lorana Bartels, senior research analyst at the Australian Institute of Criminology, says the proposed law "is not likely to have an impact on saving the lives of police officers. Most murders of police occur in the heat of the moment. In such situations people are unlikely to think about the length of the sentence they face."

She suggests that if anything, the new law could reduce conviction rates, because the accused would be less likely to plead guilty (which at the moment can attract a 25 per cent discount off a sentence). Also, it could result in juries being less likely to convict of murder, instead being "more likely to return a manslaughter verdict because they didn't think the accused deserved a mandatory life sentence. This effect has been seen with other mandatory sentences."

The new law will be deeply appealing to many police, who tend to favour more severe punishment of all crimes, including those against themselves. Is there any reason the government should want to do something to please police at this particular moment? One possible reason would be if it wanted to counter-balance less pleasing behaviour elsewhere.

As it happens, police are presently very unhappy with the government's actions over wage increases, and this has led to robust headlines such as "Police accuse O'Farrell of betrayal". Is it possible the government wants to balance offending police in this area by pleasing them in another? That might sound cynical, but there's evidence police themselves see the world in such terms.

Police Association President Scott Weber said on Sunday, "While the government is taking one step forward with the cop killer legislation, it's taking two steps back with its proposed legislation of public sector wages."