Since its beginnings in the 19th century, interstate legal assistance has undergone constant change, a development that accelerated tremendously after World War II, especially in Europe. In the course of these changes, many traditional principles of mutual legal assistance have been abolished, among them the dual criminality requirement. The aim of this project, funded by a Marie Curie Fellowship from the European Research Commission, was to analyze the scholarly bases of the dual criminality requirement in the law of mutual legal assistance, the principles from which it can be derived, and its functions.

As the re­la­tion­ships between sov­er­eignty and crim­in­al law and between cul­ture and crim­in­al law (con­flict of cul­ture or Kul­turkon­f­likt) come in­to fo­cus in the con­text of mu­tu­al leg­al as­sist­ance in crim­in­al mat­ters, this study deals in its first part with these fun­da­ment­al factors. In a second part, the re­la­tion­ship between sub­stant­ive and pro­ced­ur­al law is scru­tin­ized, and in a third part, the dual crimin­al­ity re­quire­ment is ex­amined in de­tail.

A con­clu­sion of this study is that this re­quire­ment is an in­dis­pens­able in­stru­ment of a co­oper­at­ive, in­ter­na­tion­ally-ori­ented crim­in­al justice. This co­oper­at­ive design is of great im­port­ance for a prop­er un­der­stand­ing of crim­in­al justice as cur­rently prac­ticed, as the idea of a na­tion­ally isol­ated, im­per­meable power to re­dress crime – a no­tion that is still pre­val­ent in aca­demia and prac­tice today – is a fic­tion that is be­com­ing less ten­able by the day. It is a fact and a his­tor­ic­al ne­ces­sity that sov­er­eignty evolves dy­nam­ic­ally at all times and that each en­tity with the power to re­dress crime is and must be per­meable and open to in­ter­na­tion­al de­vel­op­ments.

Ac­cord­ing to aut­ark­ic con­cepts de­veloped in the 19th cen­tury, however, sov­er­eign power to re­dress crime can only be ex­er­cised with­in na­tion­al bor­ders; hence, leg­al as­sist­ance provided to a for­eign sov­er­eign with the power to re­dress crime can only be ad­min­is­trat­ive in nature and may not ex­hib­it char­ac­ter­ist­ics of crim­in­al justice. From an ad­min­is­trat­ive law per­spect­ive such as this, it is clear that mak­ing mu­tu­al leg­al as­sist­ance de­pend­ent on dual crimin­al­ity is ob­sol­ete. This view also garners sup­port from the pre­vail­ing trend in crim­in­al law sci­ence to re­duce the sov­er­eign power to re­dress crime to the act of pun­ish­ment it­self and to ig­nore the en­tire pro­cess of le­gis­lat­ive crim­in­al­iz­a­tion and crim­in­al in­vest­ig­a­tion that pre­cedes the ju­di­cial con­vic­tion. In con­trast, the con­clu­sion reached in this study is that the power to re­dress crime should be viewed in a more nu­anced way, es­pe­cially as far as the ques­tion of sov­er­eignty and the ter­rit­ori­al area of ap­plic­a­tion is con­cerned.

Thus, the dual crimin­al­ity re­quire­ment con­tin­ues to be im­port­ant – but not for the pur­pose of isol­at­ing na­tion states and not be­cause crim­in­al law should be as­so­ci­ated with one fixed cul­tur­al en­vir­on­ment and for this pur­pose kept sep­ar­ate from oth­er cul­tures. Rather, the re­quire­ment is sig­ni­fic­ant be­cause it helps to put in­to prac­tice the rule-of-law concept that each leg­al sys­tem must have for its crim­in­al of­fenses a kal­eido­scope clearly defined by the le­gis­lature – and can only provide leg­al as­sist­ance for this defined kal­eido­scope of of­fenses. The rap­proche­ment of the states and the cor­res­pond­ing ap­prox­im­a­tion of their com­mon ef­forts to carry out law en­force­ment transna­tion­ally, there­fore, re­quire sub­stant­ive scru­tiny of ex­ist­ing dif­fer­ences among the vari­ous sys­tems of crim­in­al law. It is the dual crimin­al­ity re­quire­ment that de­mands this ex­am­in­a­tion, and it is the dual crimin­al­ity re­quire­ment that by so do­ing fosters true har­mon­iz­a­tion.