The appeals were not in front of a jury though. It makes one wonder why we have a jury in the first place. If a jury is present at the first trial then surely it makes perfect sense to use a full jury at an appeal. The reason they don't use a jury, in my opinion is that it makes a conviction less likely to be overturned. 
It makes no sense to have a jury handle an appeal. That would be like granting a second trial and granting 2 bites at the apple. That is what Italy does they have a whole second trial on appeal where both sides can make different arguments than they made at the initial trial. So if an argument failed they can learn and make a new one instead.
Under our joint Common law an appeal is decided on legal grounds.
Both sides get 1 bite at the apple, they don't get to say well my defense failed so let me change my defense or my prosecution theory failed so let's try a different argument.
The only time the defense gets another crack at it evidence wise if IF there is an argument the defense would not have been able to make at the original trial because evidence was newly discovered and the evidence is sufficient to change the outcome. The normal basis for an appeal is there was some legal error committed which if it had not been committed could have resulted in the jury acquitting.
In the US the prosecution gets no second bite the apple if there is an acquittal regardless of what new information emerges after the trial. The defendant can confess after being acquitted and there is nothing that can be done about it at that point. In the UK there are limited circumstances where there can be a retrial but it has to be based on new evidence that is compelling.
Suppose they never found the murder weapon they only had a record showing the defendant purchased a gun of the same caliber used in the murders. The defendant claimed he lost the gun and police never locate it. After being acquitted he is caught threatening someone with the gun he claimed was lost. it is ballisticly matched to the murder. That is new compelling evidence that would warrant retrying him. In the US that would not be possible though. The UK amended common law to be more in tune with the interests of justice.
It is a judge that must assess whether evidence is new or not because evidence that is not new cna't be used if you had the option of making an argument at trial but chose not to than too bad you lose it whichever side of the table you sit on. A witness changing testimony in a major way is new evidence. A new scientific principle not available at the time of the trial (like DNA) is new evidence. To warrant a new trial requires the change in testimony or other new evidence to eat at one of the pillars of the conviction. A judge must assess the legal issue of whether this burden is met.
What would legally be sufficient to overcome the suppressor? Testimony the suppressor was doctored by someone claiming to have participated in such. DNA testing of the blood that was inside which was determined to be group A blood. The defense and prosecution did not save their exhibits so there is no way to attempt to test them for DNA though chances are the tests that they conducted destroyed the DNA anyway. So the only way to try to get a retrial without the suppressor evidence would be if someone had proof the blood that was tested and determined to be group A had been planted. Short of testimony there is no way to try to establish such.
What other kind of changed testimony would be sufficient legally? A cop saying that he hear gunshots before or afte rpolice entered, a cop saying he saw her shoot herself as police entered. Something along those lines. There is no hope of anything proving that except testimony.
Since science and other evidence won't be able to attack he evidence in chief the only hope left is a change in testimony and it has to be significant enough to impeach major evidence that resulted in the jury deciding he was guilty not some minor point. In the US if an error is minor and doesn't get to the hear to the case then it is called harmless error.
Once the legal standard is met to vacate a conviction then the prosecution either gets a chance to retry the case if it wants to or if there is no case left because the new evidence is so damaging the court will in some instance not even give the prosecution the option.
One legal standard that is rarely met during a direct appeal is the clearly erroneous standard- no rational jury (or judge if it is a bench trial) could have reached the finding based on the evidence presented. This is a failsafe to prevent completely irraitonal bias. The Knox case provides a great example.
Guede testified Kercher invited him over and that while he was with her Knox came hom and when he went to the bathroom Knox and her boyfriend killed Kercher.
Knox and her boyfriend testified they were at his place all night.
The prosecution alleged Knox and her boyfriend sought out Guede, invited him to rape Kercher and help the kill her. The prosecution presented no evidence to establish when they invited him to do this, how they could have invited him since they didn't have his address, phone number or email address. The prosecution simply said he was a drug dealer and they liked drugs so they must have known how ot get in contact with him. They didn't even estbalish he ever sold drugs to them.
The court found Knox invited him over to help kill and rape Kercher.
In the US and UK this would meet the clearly erroneous legal standard. No rationally trier of fact could find based on the eivdence presented that knox invited him over to kill and rape Kercher. There was no evidence put forward to establish this happened only an unsubstantiated allegation.
Testimony from the prosecution witness that he went there on his own because he was invoted by Kercher can' possibly establish Knox invited him over. They have to at least produce evidence that she did so like showing they had shared a telephone call before where they allege she invited him. They presented nothing.
Since this is a legal standard judges decide it. Having a separate jury that could make the same mistake would be worthless.
In Italy appeal judges act as triers of fact so can be as biased and irresponsible as a jury. Her new conviction demonstrates that quite clearly. In our system appeal judges look at law and whether facts that were found had rational support and all the legal issues were all properly applied.
and their own witness claimed he was invited there by Kercher and went ove rhimself he didn't go with Knox or at her invitation.
