So if your defence is that Guede did it, then you can not advance that defence? This would seem unfair.
I believe you are correct, Sollecito and Knox were represented at the fast track trial of Guede which was also their preliminary hearing. However as you accept there were limitations on the defence case. The nature of the fast track trial was that Guede accepted prosecution evidence as given and gave up the right to challenge it. The defence were limited in there right to challenge evidence by the court as you have said. It thus seems inappropriate that the conclusions of a court where Sollecito and Knox had limited rights of challenge and cross examination can be incorporated as judicial fact subsequently. Their trial should have been effectively 'de novo'. The preliminary trial only functioning like a Grand Jury or magistrates court hearing to remand the defendants to trial, but not making any binding ruling on the subsequent trial.
The nature of the limitations the defences of AK/RS were subject to, is no different from the limitation of any other defendant.
In the Italian system, a defendant has a right to lie, but may only defend himself, not put someone else on trial.
Such limitation applies to Guede's defence as well.
I tried to point out that this is an important principle, also under other aspects.
The defences of AK & RS were not limited in their rights to challenge the evidence against them. They could even call witnesses to bring evidence against Guede, and in fact they did so, in fact they summoned Christian Tramontano and they can interrogate those witnesses. The only ting they cannot do, is interrogate the prosecution witnesses, those who are called by the prosecution to testify against Guede alone. The AK/RS defences cannot be a party directly involved in the prosecution of Guede.
The Preliminary Hearing does function somehow as a Grand Jury, and does not influence the outcome of the subsequent trial.
However that was not
only a preliminary hearing; the trial was also valid as the Guede trial, and as such, was subjected to subsequent challenges and checks from other courts, and also was picked up by another prosecution. This means that in such trial Guede did not accept the prosecution evidence as it was, and did not give up his right to challenge it. Guede only agreed to do this on a more limited set of evidence, a smaller number of witnesses.
There is a limitation inherent in short trials, this is obvious, otherwise they wouldn't be "short". The nature of short track trial is that of a compromise between the principle of completeness and the pragmatic principle of avoiding waste of money and time. So it has a nature of being limited by this compromise, cannot maximize completeness and exhaustivity. But you also should not consider it as irrelevant or inappropriate, since it has the legal status of a trial, it is a fair procedure with an actual defendant, and its outcome has some relevance.
After the trial has been checked by further magistrates and judges, its outcome is acknowledged to be final, since it was a history happening, it is also usable as element of circumstantial evidence to be assessed together with the other elements. All considerations about how convincing the scenario was and the arguments etc. can be still done, but the piece of evidence is admissible.
The conclusions of such trial are not "incorporated" as "facts", but they also cannot be dismissed as if they didn't exist. So jurisprudence says. They are a piece of circumstantial evidence which is to be considered together with the others.
By now, the presenting judicial fingdings from other trials as circumstantial evidence is not something that violates the HR Convention. You may not like this aspect of the system. But the system is soverign and legitimate. So, it's up to those who don't like it to decide not to live under the Italian jurisdiction.