I think that the credibility of Tramontano's story has to be judged primarily on other criteria - chiefly based around when and why he came forward with his story, and how generally reliable, truthful and certain he seems in his recollection.
And as I pointed out before, the jaw drops when one compares Tramontaro's story with those of people such as Curatolo and Quintavalle. In the latter case in particular, the Kercher case - and the photos/info of Knox and Sollecito - had been flooding the Italian national media (never mind just local media) for nigh-on a year when Quintavalle came forward with his miraculous "remembrance", down to the eye colour of the utterly unremarkable (at the time) woman he claims he remembers seeing in his store, the clothing she was wearing, and the direction in which she headed after leaving the store. And in addition, of course, Quintavalle had already been explicitly questioned by the police shortly after the murder, with no apparent recollection at that point. It's abundantly clear that Quintavalle's story must reasonably have been deemed utterly incredible and unreliable by any competent court - as the SC subsequently had to correct.
On the issue of the leaking of information, I would imagine that there's a long-standing series of commercial relationships between police and/or PMs and certain media outlets, in pretty much every single large town and city in Italy. The police/PM feed the chosen media outlets juicy details from high-profile current investigations, in return for cash in an envelope.
That's certainly what appears to have happened at an almost epidemic level in the Kercher case. A lesser version of it went on in the UK for years, notably between certain Met Police detectives and certain tabloid newspapers. And from what I know of Italy vs the UK, I find it almost impossible to believe that their levels of corruption in this area were anything other than a lot more widespread and entrenched.
