The US Supreme Court [official website] ruled [opinion, PDF] 6-2 Thursday in Puerto Rico v. Sanchez Valle [SCOTUSblog materials] that the double jeopardy clause [Cornell LII backgrounder] bars Puerto Rico and the US from successively prosecuting a single person for the same conduct under equivalent criminal laws. In an opinion by Justice Elena Kagan, the Supreme Court held that, for the purposes of double jeopardy, Puerto Rico is not a separate sovereign:

To determine whether two prosecuting authorities are different sover­eigns for double jeopardy purposes, this Court asks a narrow, historically focused question. The inquiry does not turn, as the term “sovereignty” sometimes suggests, on the degree to which the second entity is autonomous from the first or sets its own political course. Rather, the issue is only whether the prosecutorial powers of the two juris­dictions have independent origins—or, said conversely, whether those powers derive from the same “ultimate source.” … In this case, we must decide if, under that test, Puerto Rico and the United States may successively prosecute a single defendant for the same criminal conduct. We hold they may not, because the oldest roots of Puerto Rico’s power to prosecute lie in federal soil.

Justice Ruth Bader Ginsburg filed a concurring opinion, joined by Justice Clarence Thomas. Thomas also filed a separate concurrence. Justice Stephen Breyer filed a dissenting opinion, joined by Justice Sonia Sotomayor.

Two men, Luis Sanchez Valle and Jaime Gomez Vasquez, were charged with violating a local Puerto Rican law criminalizing the sale of firearms without a license. Prior to trial, both men were independently charged under similar federal laws. Both men were found guilty on the federal charges and sought dismissal of the local charges, arguing double jeopardy. The Supreme Court heard oral arguments [JURIST report] in the case in January.