For most judges, you rarely need to think about mens rea in deciding probable cause or in drafting jury instructions. But when you do need to think about it, the issue can be confounding.
One resource is a recent posting by Alex F. Sarch (University of Southern California – Center for Law and Philosophy) Condoning the Crime: The Elusive Mens Rea for Complicity on SSRN.
Here is the abstract:
There is a long history of disagreement about what the mens rea for complicity is. Some courts take it to be the intention that the underlying crime succeed, while others take mere knowledge of the underlying crime to be sufficient. Still others propose that the mens rea for complicity tracks the mens rea of the underlying crime — the so-called “derivative approach.” However, as argued herein, these familiar approaches face difficulties. Accordingly, we have reason to continue our search for the elusive mens rea for complicity. This paper develops a new account of the mens rea for complicity, drawing on an older approach informed by agency law principles. In particular, I argue that a distinct attitude of condoning the underlying crime is best seen as the mens rea for complicity. This approach yields a more principled framework for determining when accomplice liability is warranted than existing approaches. Moreover, it demonstrates that certain reforms to the current legal regime are warranted: most importantly, that a distinction between full and lesser complicity be recognized.