SCOTUSblog has the details:
After oral argument, the outcome in Henderson v. United States wasn’t really in doubt. The entire Court had expressed skepticism of the idea that a firearm owner convicted of a felony couldn’t lawfully sell his weapons on the open market, or transfer them to an independent third party. Today, in a crisp eight-pager by Justice Elena Kagan, the Court unanimously ruled in favor of the firearm owner. Along the way, the Court ironed out some significant legal wrinkles. Of special note, the Court clarified that felons can be entitled to the benefits of equity in federal court.
When an individual surrenders his firearms to police and is later convicted of a felony, what happens to the firearms? The weapons can’t go back to the felon, because federal law prohibits felons from possessing firearms. Yet the felon still owns the weapons, which could have considerable financial, sentimental, or historical value. Understandably enough, many felons in this situation would like to sell or transfer their firearms, rather than let Uncle Sam indefinitely possess them. The question before the Court in this case was whether federal law gave felons that right to transfer.
In the decision under review, the U.S. Court of Appeals for the Eleventh Circuit had ruled against transfer based on a broad view of “constructive possession” – roughly, the idea that someone can lack physical possession of an object but still exert enough control over it to count as possession for purposes of law. The court of appeals had also seemed to say that a convicted felon lacked “clean hands” and so could not take advantage of any form of equitable relief, including equitable transfers of property.
Today, however, the Supreme Court unanimously ruled in favor of the firearm owners by allowing them to transfer their weapons to independent third parties, including to have the weapons sold on the open market. As Justice Kagan succinctly explained, this is a pragmatic solution that accords with the statute’s text and purpose, and also has the benefit of fitting snugly with common sense.