A defendant stands in the dock. An expert describes them as a “psychopath”. In an instant, one word threatens to eclipse their history, circumstances and the crime itself.

In Ireland, England and Wales, judges are not supposed to add years to a sentence because someone has been described as a psychopath. But the label can still enter criminal justice through expert reports, risk assessments, parole, mental disorder cases and preventive detention.

In the US, the Psychopathy Checklist-Revised (PCL-R) – an assessment tool used for diagnosing psychopathic traits – has been used in death penalty cases, parole hearings, preventive detention and pre-sentence evaluation. These cases usually concern future risk, with evidence most often introduced by the prosecution or state. Research from the US has shown a marked increase in the use of PCL-R over time.

The “psychopath” label has been applied in a number of cases involving adolescent offenders, and occasionally raised by the defence, alongside brain-imaging evidence, to argue for reduced culpability or impaired control.

In the 1980s case of American serial killer Brian Dugan, psychopathy and brain-imaging evidence were used to argue that he could not control his “killer impulses”. He was ultimately sentenced to death in 2009, but the testimony transformed it from a “slam dunk for the prosecution into a much tougher case”.

In Scotland, where an order for lifelong restriction (an indeterminate, lifelong sentence for serious violent or sexual offenders assessed as posing a continuing risk) is considered, the High Court can commission a risk assessment report. Psychopathy may be........

© The Conversation