Lord Thomas has claimed that Internet pornography was ‘a contributing factor in one of the most gruesome murder cases he had to rule on last year’ (see also the Daily Telegraph). As someone who has to sit in judgement over some of the worst offences committed in the United Kingdom, his position is understandable. But it goes against the best evidence we have: Internet porn does not cause more violence against anybody. While convicted murderers often have large collections of violent images, pornography does not turn people into murderers. A great many ordinary members of the public, including men and women, with no interest in harming anyone possess images that have violent themes.
We can be confident of this claim in the United Kingdom because Internet use has expanded significantly over the last two decades while homicide rates, and other related crimes of domestic violence are significantly down. Figure 3 (page 10) of the Home Office’s report, Focus on: Violent Crime and Sexual Offences, 2011/12, shows that many of these key crime types peaked in the early 90s, well before the Internet was a significant cultural phenomenon. Note that these statistics are probably best at identifying trends in offences because they are comparable from year-to-year but are not necessarily as good at estimating underlying prevalence for which there is still much uncertainty because of the difficulty of interpreting survey results.
Correlation does not imply causation, but dis-correlation is a strong count against causation. When Internet use (including porn use) is going up significantly, and the murder and assault rate is going down, we can be confident that the Internet is not a contributing factor to the murders that do take place. This position is backed up by academic scholarship that looks at crime trends the world over.
Evidence of pornography use plays two key roles in murder trials. The first is by prosecutors attempting to establish a motive for the killing. The inferences here are difficult but potentially legitimate if they help to bring a murderer to justice. The second, much less justified, is by defence counsel in mitigation in order to argue for a lesser sentence. Defences sometimes claim that (fictional) media bears some of the responsibility for the murder. Sometimes they claim that the offender started by suffering an addiction to pornography, a diagnosis with no scientific basis, to suggest that porn impaired the judgement of the offender, or provoked them in some way.
The statistical evidence suggests that these claims are unjustified: a murderer stands alone in the dock. They cannot claim that their actions were commissioned by the media they consumed. So on this count, it was right that the murderer Lord Thomas was hearing lost his appeal against a whole life tariff.