People are appalled and fascinated by crime in equal measure. Most
of us aspire to live in a safe, crime-free society, yet we’re gripped by
books and films about murderers, bank-robbers and sadists. In real
life and in fiction, such tales often involve forensic psychologists who
are responsible for assessing and treating criminals with mental-
health problems. Sometimes they also advise the police as criminal
profilers and hunters (as in the British TV series Cracker), an activity
that particularly captures the public imagination. Psychologists also
research many issues related to criminal behaviour and the criminal-
justice system. Are jurors influenced by a defendant’s choice of
clothes? What makes a person make a false confession? Can the police
be trained to tell whether a suspect is lying? How accurate is eyewit-
ness memory?
A life of crime
Whether it’s two minutes in an illegal parking spot or a mildly exagger-
ated insurance claim, many of us will have decided momentarily that
the advantages to rule-breaking outweigh the potential costs. However,
these minor transgressions aside, the majority of us live according to the
rule of law most of the time, with due consideration of other people’s
interests as well as our own. It’s actually a tiny proportion of persistent
offenders who commit nearly all crimes, especially the most serious ones.
The psychologists Terrie Moffit and Avshalom Caspi, of the University
of Otago in New Zealand, have established that this criminal minority
can be divided into two distinct subgroups, based on their research
following the lives of a large sample of people born in Dunedin in 1972.