What constitutes a criminal offence?

Two elements are necessary in order for a defendant to be found guilty of committing a criminal offence. They are the Actus Reus and Mens Rea. Actus reus translates to 'guilty act', it is the action of the crime itself, e.g. pulling the trigger of a gun in order to shoot someone. Mens Rea, however, is the intention of a defendant whilst committing the crime e.g. carrying a gun with the intention of shooting someone. In order for a defendant to be found guilty, it must be proven by the prosecution that the defendant had both the Actus Reus and Mens Rea for that particular offence. If the prosecution fail to adequately prove the existence of both elements the defendant may have a defence leading to a lighter sentence or even acquittal.