Introduction: Several studies have shown an association between homicide and sexual chromosomal abnormalities, but data are still lacking regarding Klinefelter syndrome. Methods: We retrospectively reviewed two cases of homicide perpetrators who were both diagnosed with Klinefelter syndrome on the basis of a karyotype analysis. A neurocognitive assessment was also performed (MMSE, Frontal Assessment Battery, brain CT, and electroencephalogram). Results: Numerous intermediate risk factors of homicide were shared by our two cases, including dispositional (male gender, young age, low socioeconomic status), historical (prior arrest record and past conviction for any offense), contextual (unemployment), and clinical (alcohol abuse). Conclusion: It is important that clinicians go beyond obvious risk factors, such as chromosomal abnormalities, to pinpoint other meaningful risk factors and potentially facilitate preventive approaches.