Leakage Behaviour: An Undervalued Forensic Construct

Nathan Brooks

Leakage or warning behaviour refers to the intentional or unintentional divulgence of motivation, capability, intent, or resolve to commit a violent or terrorist attack by a ‘would be’ perpetrator (Meloy & O’Toole, 2011). These expressions, most evident in interpersonal dealings, can be essential for the early detection of concerning behaviours. Leakage behaviour occurs for a variety of reasons, including, excitement, attention seeking, a sense of accumulating power, a desire to frighten or intimidate, or a sudden sense of resolve or meaning (Meloy & O’Toole, 2011). This behaviour can occur through verbal communication and deliberate or unintentional behaviour in both daily living and online activity. For example, Man Heron Monis displayed a number of observable or ‘leakage’ type behaviours prior to the attack which signalled his intent, most notably on 17 November 2014 – approximately a month prior to the attack – pledging his allegiance to ISIL on his website (State Coroner of New South Wales, 2017). While forensic risk and threat assessment tools have established risk factors that guide risk estimates and inform decision making, these instruments are only as strong as the information used for consideration. This requires not only sound clinical interviewing skills, but also competent risk and threat knowledge applicable to the presenting concern. Practitioners tasked with treating or assessing an at-risk person, must determine the threshold whereby leakage is suggestive of an overt act of violence rather than an indirect threat. This entails determining credibility, direct implications, and other associated warnings signs that may indicate a specific intention or target. The presentation will examine the importance of leakage behaviour in risk and threat assessment, exploring case examples, and providing recommendations to incorporate leakage behaviour into forensic practice.


Nathan is a Senior Lecturer with Central Queensland University and a Consultant Forensic Psychologist working in the criminal justice sector. He has experience in both the private and public sectors, particularly working with high-risk and high-harm offenders. His areas of expertise include personality testing, crime analysis, risk management, and psychological assessment.

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