Sentence:  As a general rule the act (or omission) causing death and the relevant <WSD>mens rea</WSD> must occur at the same time. The most obvious application of this rule to exclude liability is the case where the <WSD>mens rea</WSD> is formed after the actus reus has taken place. 
Meaning of the word marked with <WSD> tags:  A guilty mind, the conscious knowing of a perpetrator while committing an act that the act is illicit.