Research indicates individual pathways towards school attacks and inconsistent offender profiles. Thus, several authors have classified offenders according to mental disorders, motives, or number/kinds of victims. We assumed differences between single and multiple victim offenders (intending to kill one or more than one victim). In qualitative and quantitative analyses of data from qualitative content analyses of case files on seven school attacks in Germany, we found differences between the offender groups in seriousness, patterns, characteristics, and classes of leaking (announcements of offences), offence-related behaviour, and offence characteristics. There were only minor differences in risk factors. Our research thus adds to the understanding of school attacks and leaking. Differences between offender groups require consideration in the planning of effective preventive approaches.