Actus non facit reum nisi mens sit rea implies that:

Actus non facit reum nisi mens sit rea is a Latin maxim that forms a fundamental principle of criminal law.
Definition: It translates to "the act does not make a person guilty unless the mind is also guilty." This means that for a crime to be committed, there must be both a guilty act (actus reus) and a guilty mind (mens rea).

Option D: No act per se is criminal unless accompanied by a guilty mind is the correct answer.
This option accurately reflects the principle of actus reus and mens rea. A criminal act requires not only the commission of a prohibited act (actus reus) but also the presence of a blameworthy mental state (mens rea). The mens rea varies depending on the crime, ranging from intention to recklessness or negligence. Without the requisite mens rea, even if the actus reus is present, a person cannot be convicted of a crime.

Why other options are incorrect:
Option A: This statement is incorrect because it emphasizes only the actus reus, ignoring the essential element of mens rea. Simply performing an illegal act is not sufficient for criminal liability; the accused's mental state must also be considered.
Option B: This option is also incorrect because while motive might be relevant in some cases to determine sentencing, it's not sufficient for criminal liability. The focus should be on the mens rea directly related to the crime, not just a general motive.
Option C: This option is also incomplete because simply having a guilty mind (mens rea) and a desire to act on it is insufficient. The actus reus, the actual commission of the prohibited act, is also necessary for criminal liability.