1. When was the principle of 'sine qua non' as a key element of actus reus formally recognized in modern criminal law doctrine?
In the 19th century during the codification of criminal law
Explication
The principle of 'sine qua non' as a fundamental element of actus reus was notably recognized during the 19th century, a period marked by the formal codification and development of modern criminal law doctrines. This period saw increased emphasis on establishing clear legal principles, including the necessity of actus reus for criminal liability.