<p>I don’t know about the FBI’s take on the law but possession is not a crime that can be shared out like taking part in an armed robbery. Let’s say the drugs are found in the trunk or glove compartment. A guy in the back seat is in possession how? He isn’t. If the drugs were tossed on the floor, then the police will wonder who they belong to - and they will use the threat of arrest to find out. That’s the point. If they don’t know who the drugs belong to, then they try to figure it out and everyone in the car is suspect. But if you’re at a party and you don’t live there, then they have no legal way of alleging that you were in possession of drugs found at the house unless they can directly connect you to them.</p>
<p>It’s always possible the police may arrest you but the prosecutors who have to file charges would need to be dumb to charge people at a party when some guy at the party had drugs on him.</p>