Jamie killed Katie in Adolescence due to a combination of factors including his lack of self-esteem, perceived bullying at school, and radicalization through online incel propaganda. Jamie had asked Katie out after a topless photo of her was circulated as revenge porn, but she rejected him and publicly called him an incel, which triggered his violent response. The series explores Jamie's internal struggles with masculinity, self-worth, and misogynistic influences that led him to commit the murder. His crime is not depicted as that of a cold psycho but rather as a result of the complex social and psychological challenges faced by today's youth, exacerbated by online radicalization and lack of support and understanding at home and school. Jamie initially denies the crime due to shame but comes to accept his guilt later in the series.