In Claiborne v. U.S., case no. No. 065618 (June 4, 2007), the U.S. Supreme Court decided that the death of the petitioning criminal defendant rendered the case moot, and thus it vacated the judgment of the Eighth Circuit Court of Appeals that had reversed the district court’s downward adjustment from the federal sentencing guidelines. The order itself tells you nothing about the case, so I suggest you start with Kimberly A. Kralowec at The Appellate Practitioner, who provides a brief rundown, from which it makes sense next to check this SCOTUSBlog post from before the ruling, describing efforts by a similarly situated petitioner to save the Claiborne case despite its technical mootness.
Columbia law professor Michael Dorf uses the Claiborne case as a starting point for a short Findlaw article on the wider subject of the role of the Supreme Court and tensions in justiciability doctrine, A Mootness Dismissal Illustrates the Supreme Court’s Split Personality: Is it a Constitutional Court or a Court of Error? The article describes the underlying issue in Claiborne, examines whether other rules might have saved the Claiborne case, argues that the Supreme Court should not be subject to the same strict justiciability standards of lower federal courts, and compares the more liberal justiciability standards of courts of last resort in some other countries. All this in a very readable 1900 or so words.