Criminal offenders regularly face negative reactions from the public, which may be even stronger if the offender suffers from a mental disorder and/or illness. The aim of this study is to examine the influence of the type of criminal offense and the type of mental disorder or illness diagnosis on the attribution of responsibility, intensity of emotions, recidivism expectations and social distance towards the offender. A 2×3 independent experimental design was implemented. The first independent variable is the type of criminal offense, with two levels: theft and attempted murder. The second independent variable is the type of diagnosis, with three levels: no mental disorder diagnosis, major depressive disorder and schizophrenia. For the purpose of experimental manipulation, a case description text was designed. Data were collected online, with 315 adults participating in the study. The results indicate that the type of diagnosis affects the attribution of responsibility. Less responsibility is attributed to the offender when they suffer from schizophrenia compared to major depressive disorder or no diagnosis. The type of diagnosis also affects the intensity of emotions. The lowest levels of empathy, pity and fear are observed in cases without a diagnosis or with major depressive disorder, compared to schizophrenia. The opposite pattern is observed in the intensity of anger, which is lowest in cases involving schizophrenia, compared to major depressive disorder or the absence of a diagnosis, where it is highest. Furthermore, participants expect lower recidivism when the offender has no diagnosis or has major depressive disorder compared to schizophrenia. Finally, the type of diagnosis does not affect the assessment of social distance.