This page brings together scientific research and academic publications concerning adolescent brain development, mental health and criminal responsibility.

The materials explore how young people's development, psychological wellbeing and other factors may be relevant to understanding behaviour and sentencing.

These publications provide wider research context. They do not, by themselves, establish what caused Carly Gregg's actions or determine the legal questions in her case. Visitors are encouraged to read the original studies and consider their findings and limitations.

Mental Health and Neurodevelopmental Disorders, Criminality, and Criminal Responsibility

Explore the connection between mental health and neurodevelopmental disorders, criminality, and criminal responsibility. 

The Developmental Perspective on Juvenile Justice — Why Children's Maturity Matters

In this academic paper, developmental psychologist Laurence Steinberg examines how decades of research into adolescent psychological and brain development have influenced the way young people are treated within the criminal justice system.

The paper discusses the developmental approach to juvenile justice, including its influence on Restatement of Children and the Law, which considers how legal principles should account for the differences between children and adults.

Carly Gregg was just 14 years old when the events occurred. This research provides important context for understanding why a child's developmental maturity should be considered when evaluating responsibility, sentencing and opportunities for rehabilitation.

A developmental approach does not mean ignoring the seriousness of an offence or removing accountability. It recognises that young people are still developing and that their capacity for judgement, self-regulation and change differs from that of fully mature adults.

The paper offers a broader perspective on juvenile justice policy. It does not determine the appropriate legal outcome in Carly's individual case.

Why Adolescent Brain Development Matters in Sentencing

Neuroscientific research into adolescent brain development shows that the brain systems involved in emotional responses, impulse control, risk assessment and long-term planning continue to develop throughout adolescence and into early adulthood.

During adolescence, heightened sensitivity to emotions and rewards can interact with still-developing abilities to regulate behaviour and consider long-term consequences. These developmental differences are important when considering a young person's culpability, circumstances and potential for rehabilitation.

The Late James Garbarino Professor Emeritus

Education Ph.D., Cornell University 

The following biographical statement describes Professor Garbarino's research interests and professional experience. It is reproduced as a historical account of his work.

My research focuses on issues in the social ecology of child and adolescent development. I have a long standing interest in a wide range of violence-related issues - war, child maltreatment, childhood aggression, and juvenile delinquency. In 1991 I undertook missions for UNICEF to assess the impact of the Gulf War upon children in Kuwait and Iraq, and have served as a consultant for programs serving Vietnamese, Bosnian and Croatian children. I also serve as a scientific expert witness in criminal and civil cases involving issues of trauma, violence, and children. In all these issues I am concerned with how developmental processes are shaped by the human ecology in which they occur, and have a particular interest in matters of spirituality and identity in this process. After completing a project on physical aggression in girls (resulting in a book entitled See Jane Hit: Why Girls Are Growing More Violent and What We Can Do About It), I am currently working on a project dealing with childhood in the face of the terrorist threat.

Selected Publications by Professor James Garbarino

Garbarino, J. and DeLara, E. (2002) And Words Can Hurt Forever: How to Protect Adolescents from Bullying, Harassment, and Emotional Violence (NY: Free Press, 2002

Garbarino, J. and Bedard, C. (2001) Parents Under Siege: Why You Are the Solution, Not the Problem, in Your Child's Life. NY: Free Press.

Garbarino, J. (1999) Lost Boys: Why Our Sons Turn Violent and How We Can Save Them. (NY: Free Press).

Garbarino, J. (1995) Raising Children in a Socially Toxic Environment (1995). San Francisco: Jossey-Bass Publishers.

Academic Research — Adolescent Development and Criminal Responsibility

This influential academic paper by Laurence Steinberg and Elizabeth S. Scott examines how developmental immaturity affects young people's judgement, decision-making and criminal responsibility.

Although the paper focuses on juvenile capital punishment, its discussion of adolescent development provides important background for wider questions about youth sentencing, accountability and rehabilitation.

The research is provided for educational context and does not establish the legal outcome of Carly Gregg's case.

Juvenile Justice Policy and Practice — A Developmental Perspective

This academic paper by Kathryn Monahan, Laurence Steinberg and Alex R. Piquero examines how research into adolescent development has influenced approaches to juvenile justice, particularly the balance between punishment and rehabilitation.

The authors discuss how young people's decision-making, brain development and capacity for change differ from those of adults. They also explore how developmental research has contributed to changes in juvenile sentencing policy and legal thinking.

Carly Gregg was only 14 years old when the events occurred. This research provides important context for considering how a child's age, psychological maturity and potential for rehabilitation should inform discussions about criminal responsibility and punishment.

The paper highlights why rehabilitation remains an important consideration in juvenile justice, even when an offence is extremely serious. Recognising developmental differences does not mean removing accountability or overlooking the devastating loss of Ashley Gregg's life.

This research offers a broader scientific and policy perspective. It does not determine the appropriate sentence or legal outcome in Carly's individual case.

Adolescent Development — Accountability, Rehabilitation and the Capacity for Change

In this 2012 interview published in Science, developmental psychologist Laurence Steinberg discusses how research into adolescent brain development helped inform landmark US Supreme Court decisions concerning the punishment of young offenders.

Steinberg explains that adolescents should be held accountable for serious offences, but their developmental immaturity must also be recognised. Young people are still changing psychologically and neurologically, and their behaviour during adolescence does not necessarily predict who they will become as adults.

This is particularly relevant to Carly Gregg, who was just 14 years old when the tragedy occurred. The seriousness of her actions must be acknowledged, but so must her developmental immaturity and potential for rehabilitation.

Steinberg also highlights the difficulty of predicting whether a young person who commits a violent offence will continue to behave violently in adulthood.

A terrible act committed at 14 should not automatically be treated as proof of an unchangeable character or a lifetime of dangerousness.

This interview provides important scientific context for considering juvenile sentencing, accountability and the possibility of personal growth. It does not determine Carly's individual risk, rehabilitation prospects or legal outcome.

Juveniles’ Competence to Stand Trial — Why Age and Understanding Matter

This important academic study by Thomas Grisso, Laurence Steinberg and colleagues examines whether adolescents possess the same abilities as adults to understand criminal proceedings, make informed legal decisions and assist their lawyers in preparing a defence.

The researchers assessed 927 adolescents and compared their abilities with those of 466 young adults. Their findings identified significant developmental differences, with younger adolescents particularly likely to experience difficulties in abilities relevant to competence to stand trial.

Carly Gregg was just 14 years old when the events occurred and 15 when she stood trial. This research raises important questions about how a young teenager understands complex legal proceedings, evaluates advice and participates in decisions that may affect the rest of their life.

Competence to stand trial is distinct from criminal responsibility. It concerns whether a defendant can understand the proceedings and assist in their defence, rather than whether they were responsible for the offence itself.

This study does not establish that Carly was legally incompetent to stand trial. Such a determination requires an individual legal and clinical assessment. The research demonstrates why developmental maturity deserves careful consideration when children face serious criminal proceedings.

Neuroscience and the US Supreme Court — Why Adolescent Maturity Matters

In this academic paper, developmental psychologist Laurence Steinberg examines how scientific research into adolescent brain development influenced landmark US Supreme Court decisions concerning the criminal responsibility and punishment of young people.

The research explains how adolescents differ from adults in psychological and neurological maturity, and why these differences are relevant when courts consider culpability and sentencing.

Carly Gregg was only 14 years old. This research provides important context for understanding why her developmental age matters when considering responsibility, punishment and the potential for rehabilitation.

Recognising adolescent immaturity does not remove accountability for serious offences. It means acknowledging that children are still developing and should not automatically be judged according to the same expectations as fully mature adults.

The paper provides a scientific and legal perspective on juvenile justice. It does not determine the legal outcome of Carly's individual case.

Adolescent Cannabis use and Risk of Psychotic Bipolar Disorders

This 2026 study, published in JAMA Health Forum, examines associations between adolescent cannabis use and the subsequent diagnosis of psychotic, bipolar, depressive and anxiety disorders.

The research provides important context for understanding adolescent mental health and potential risk factors. However, an association does not establish that cannabis use caused a particular psychiatric condition, nor does this study establish what happened in Carly Gregg's individual case.

The original research paper is provided below for visitors to examine its findings and limitations.

Carly's Journal — Understanding the Wider Context

During Carly Gregg's trial, evidence concerning vaping and her mother's search for vapes became part of the account of events leading up to the tragedy of 19 March 2024.

However, Carly's journal provides additional context that should not be overlooked.

In an entry dated 12 March 2024, just one week earlier, Carly described emotional distress, feelings of numbness, anger and regret, and an experience she herself referred to as a possible psychotic break. She also wrote positively about therapy and her efforts to manage her feelings.

These writings do not establish a medical diagnosis or explain precisely what happened on 19 March. Nor do they prove that cannabis use caused or prevented any particular symptoms.

They do, however, raise important questions about Carly's emotional wellbeing, the difficulties she was experiencing and whether those circumstances were fully understood.

Reducing the events of that day to a dispute about vapes risks overlooking this wider context. Understanding the tragedy requires careful consideration of the evidence, including Carly's age, mental health history, journal writings and the testimony presented at trial.

Young Adulthood as a Transitional Legal Category — Development, Maturity and Justice

In this academic paper, Elizabeth S. Scott, Richard J. Bonnie and Laurence Steinberg examine how scientific research into brain development, psychological maturity and social change has challenged traditional assumptions about adulthood within the criminal justice system.

The authors explore whether young adulthood should be recognised as a distinct developmental stage in law and justice policy, rather than assuming that everyone becomes fully mature upon reaching the age of 18.

Although this paper focuses primarily on young adults rather than younger adolescents, it provides important wider context for Carly Gregg's case. Carly was only 14 years old when the events occurred, an age at which developmental maturity is an especially important consideration.

The research highlights why age, maturity and capacity for change deserve careful attention when considering criminal justice responses. It also contributes to wider discussions about proportionate punishment and opportunities for rehabilitation.

Recognising developmental differences does not diminish the seriousness of Ashley Gregg's death or remove the need for accountability. It encourages a justice system that considers both the harm caused and the developmental stage of the person responsible.

This paper provides broader scientific and policy context. It does not establish the appropriate legal outcome in Carly's individual case.