Must State Police Return Wrongfully Seized Marijuana?

Imagine the following scenario. P is a local police officer who stops D for speeding. In the course of a consensual search of D’s car, P finds a small bag of marijuana. State law bans the simple possession of marijuana by most people, so P seizes the drug. However, D subsequently convinces a judge that he was allowed by state law to possess the marijuana (say, because he’s a qualified patient under the state’s medical marijuana law). Following the judge’s ruling, D asks P to return the marijuana. Must P do so?

Over at Prawfsblawg, I explain why this question is so difficult to answer – and at least four different ways courts could go about answering it.