Going back in time is difficult in the real world. But we do it in the judiciary all the time.
For example, ever since the Supreme Court in Booker held that the sentencing guidelines were advisory, the Ninth Circuit has conducted what we call "limited Ameline" remands, in which the district court is basically asked whether -- for those cases that were on appeal when Booker was decided -- it would have imposed the same sentence had it known the guidelines were advisory. The answer is typically "yes", and regardless of the accuracy of that retrospective prediction, at least we give the defendant a shot.
The question in this case is whether the district court can take into account post-sentencing conduct in such remands. And Judge Thompson concludes, entirely reasonably, that it cannot, at least for purposes of answering the question "would your sentence have been different at the time had you known the guidelines were advisory?" We're trying to figure out what you would have done. Adding events after the date in question aren't relevant to that inquiry.
Other circuits do it differently, and at some point, I think the Supreme Court should take the issue up. More accurately, I think they should have taken the issue up, since at this point, the number of pending-Booker cases is rapidly diminishing, and the appellate process for most of these cases has already concluded. But given the way the Ninth Circuit does it -- with limited remand, not a full resentencing -- Judge Thompson's decision seems correct. As a temporal matter, we're asking what you would have done then, not what you'd do now.
Now, Judge Thompson doesn't hold that post-sentencing events are always irrelevant, only that they're not relevant to the first prong of the Ameline inquiry: whether or not the judge would have given the same sentence. The panel expressly doesn't decide whether post-sentencing conduct is relevant in the minority of cases in which the district court responds that its sentence would indeed have been different had it known the guidelines were advisory. That's a more difficult question, and one for another day.
So here, the district court doesn't get to take into account the defendant's alleged rehabilitation after his sentence was handed down. Again, this seems right if you accept the predicates of the Ninth Circuit's limited Ameline procedure. I'll also add something that Judge Thompson does not mention: it would seem a bit untoward to do otherwise in the event the post-sentencing conduct was unfavorable. Imagine, for example, the defendant committed an assault in prison post-sentencing, and the district court said: "I know you filed an appeal, and got a remand under Ameline to see if I'd do the same thing. Given your recent crime, however, I feel like giving you an extra couple of years. Congratulations on winning in the Ninth Circuit." There's something about that that doesn't feel entirely kosher. And a one-way rachet in post-Ameline remands doesn't seem fair either.
So I'm on board for this one. When you go back in time, let's really go back in time. No peeking into what subsequently transpired.