Insanity definition and the threshold for satisfying its legal criteria tend to vary depending on the jurisdictions. Yet, in Western countries, the legal standards for insanity often rely on the presence of cognitive and/or volitional impairment of the defendant at crime time. Despite some efforts having been made to guide and structure criminal responsibility evaluations, a valid instrument that could be useful to guide forensic psychiatrists' criminal responsibility assessments in different jurisdictions is lacking. This is a gap that needs to be addressed, considering the significant forensic and procedural implications of psychiatric evaluations. In addition, differences in methodology used in insanity assessments may also have consequences for the principle of equal rights for all citizens before the law, which should be guaranteed in the European Union. We developed an instrument, the Defendant's Insanity Assessment Support Scale (DIASS), which can be useful to support, structure, and guide the insanity assessment across different jurisdictions, in order to improve reliability and consistency of such evaluations.