Which assumes there was tampering and not just "new evidence" as you claimed
Well, if you want to play semantics, if witness tampering is proven then the previous ruling can be invalidated.
Only if the verdict was guilty. Not the other way around. Even lolwiki
suggests that you're wrong:
This principle does not prevent the government from appealing a pre-trial motion to dismiss or other non-merits dismissal, or a directed verdict after a jury conviction, nor does it prevent the trial judge from entertaining a motion for reconsideration of a directed verdict, if the jurisdiction has so provided by rule or statute. Nor does it prevent the government from retrying the defendant after an appellate reversal other than for sufficiency, including habeas, or "thirteenth juror" appellate reversals notwithstanding sufficiency on the principle that jeopardy has not "terminated." There may also be an exception for judicial bribery, but not jury bribery.
If jury tampering isn't sufficient cause for retrying an acquittal, I'd be shocked if witness tampering would be. The general trend is that you have the evidence you have, the witnesses you have, and the jury you have. If those result in acquittal, it's done.
The followup wiki
sheds even more light (and addresses this specific case I believe):
Retrial is not possible if the verdict is overturned on the grounds of evidentiary insufficiency, rather than on the grounds of procedural faults. As noted above, if the trial court made a determination of evidentiary insufficiency, the determination would constitute a final acquittal; in Burks v. United States 437 U.S. 1, (1978), the Court held that "it should make no difference that the reviewing court, rather than the trial court, determined the evidence to be insufficient."
So it appears to directly state that in the US, this case could not be subject to retrial. So we're kinda back to Italy allowing a case of double jeopardy that our own laws would not allow.
I think I know where your confusion is, and it is my fault. I should have pointed out that they can be retried under different charges, and not just left it as retried.
Huh? Given that no one's even broached the subject (and it's not applicable here), I'm going to go with you realizing you're wrong and are just pulling stuff out of your ***.