The aim of this study was to examine the relationship between socio-demographic characteristics of participants, experiences with mentally ill persons and criminal offenders, criminal victimization experiences, diagnosis of mental illness and attitudes towards mentally ill persons together with attitudes towards the insanity defense, assessments of dangerousness and (in)sanity characteristics and type of punishment for perpetrators of actual criminal cases. Using an online survey, data were collected on a convenient sample of 263 adult participants, with an average age of 30 years (23.6% of men). Participants showed relatively high tolerance and low prejudice against the mentally ill persons and had relatively little experience with the mentally ill persons, offenders, criminal victimization, and diagnosed mental illnesses. Participants were exposed to a description of one of the three actual criminal offense cases. Based on the read description of the given criminal case, they assessed the (in)sanity and dangerousness of the offender and the adequate punishment for the committed offense. Also, they estimated the offender’s responsibility for the committed offense and towards the insanity defense. Their estimates varied depending on the case read, and the most consistent and highest contributions in explaining criteria variables were obtained for the type of participants’ occupation and the level of prejudices towards mentally ill persons. Participants in helping occupations and those expressing lower prejudice considered the offender to be more not guilty by reason of insanity (NGRI), less dangerous, less responsible for the committed act, and they considered that the defense was less abused by insanity defense.