Justice Alito hasn't been on the U.S. Supreme Court very long. His decision today in the case of Holmes v. South Carolina is his first decision, and he writes for a unanimous court.
In substance, the Supreme Court invalidates a South Carolina rule that prevented criminal defendants, in this case an individual sentenced to death for murder, from introducing evidence that someone else committed the crime and confessed to it, if the judge thinks that the prosecution has a solid case based on physical evidence. The defendant was arguing that this forensic evidence had been the subject of tampering. The flaw in this rule, the high court notes, is that the judge isn't meaningfully examining the defendant's argument that the prosecution physical evidence is flawed.
Perhaps the most notable element of the decision is that it is long on logic and thin on authority. It isn't hard to conclude that the ultimate decision is the correct one. Evidence that someone else committed the crime is almost always logically relevant, and thus constitutionally mandating its admission seems essential to a fair trial in a wide variety of criminal cases. Justice Alito himself seems a bit fuzzy on which particular part of the Constitution mandates that this evidence must be available to a criminal defendant, pointing to the 14th Amendment Due Process clause and two different parts of the 6th Amendment, although not the trial by jury right, which could also be a logical basis for the ruling.
Indeed, one gets the sense, in the recitation of facts, which described a palm print on the scene where the defendant had no reason to be, tiny fibers left at the scene, and confirming DNA evidence from both blood and semen, in addition to a witness who placed the Defendant at the scene, that one reason that the Supreme Court is so comfortable setting aside this death warrant in this case is that the Court is confident that on retrial, confronted with the defendant's full defense, that a jury is almost certain to come out the same way, or that in far less likely alternative, the prosecution really does have something to be afraid of, because it really did frame the defendant.