In Cuellar v. United States, no. 06-1456, the Supreme Court (Justice Thomas writing) held that the portion of the money laundering statute that prohibits the international transportation of proceeds of unlawful activity (18 USC section 1956(a)(2)(B)(i)), requires proof that the funds were not only concealed and transported, but also that those actions were taken, at least in part, for the purpose of concealing or disguising their nature, location, source, ownership or control.

In Justice Thomas's words, "Merely hiding funds during transportation is not sufficient to violate the statute, even if substantial efforts have been expended to conceal the money." Because the evidence demonstrated that Mr. Cuellar had concealed and transported money in the floorboard of his vehicle for the purpose of paying the leaders of a drug operation (and not merely to get it out of the country), his conviction was reversed.

In a second cse, United States v. Santos,
no. 06-1005, a divided Court affirmed the judgment of the Seventh Circuit, which had upheld the grant of a 2255 motion on the ground that the word
"proceeds" as used in 18 USC sections 1956(a)(1)(A)(i) and (h) applies only
to criminal "profits" and not merely to criminal "receipts."

According to Justice Scalia (joined by Justices Souter, Thomas and Ginsburg), because both "profits" and "receipts" are ordinary definitions of the term "proceeds," and because neither definition would render the statute incoherent, redundant or utterly absurd, the rule of lenity dictates that the Court choose the definition that is "always more defendant-friendly."

Justice Stevens concurred in the judgment because no legislative history exists to define "proceeds" in the context of the underlying offense (running an illegal lottery), although he would leave the door open to allowing "proceeds" to include criminal receipts for certain underlying offenses specifically discussed in the legislative history.

Scotusblog has more on Santos.