Last month, the United States Supreme Court held in a 7-2 opinion that the government is required to demonstrate a defendant charged with unlawful possession of a firearm (a) possessed a firearm and (b) the defendant knew not to possess a firearm in the prosecution of gun possession cases. Justice Breyer wrote the majority opinion for the court. Justice Samuel Alito was joined by Justice Clarence Thomas in the dissent. It should be noted, the defendant in the matter was prosecuted under a law that bars people who are in this country illegally from possessing guns. As such, it will be interesting to see how these possession cases will be litigated in the future when not prosecuted under the above referenced law. In any event, it appears knowledge will be key in the future prosecution and defense of these cases.
In Washington State the crime of Unlawful Possession of a Firearm in the First Degree is a Class B felony punishable by up to 10 years in prison and a $20,000 fine. Unlawful Possession of a Firearm in the Second Degree is a Class C felony punishable by up to 5 years in prison and a $10,000 fine. Each firearm possessed under RCW 9.41.040 is considered a separate offense.
See this recent PBS article: