This does not seem like a leak to me, and I have been working in press for 2 decades. It looks like they decided to report it early:
http://www.guardian.co.uk/world/2011/jun/29/amanda-knox-dna-evidence-contaminatedAmanda Knox DNA evidence contaminated, appeal court hears:
Experts brand as unreliable the key evidence that Raffaele Sollecito's DNA was found on victim Meredith Kercher's bra
The appeal by Amanda Knox and her Italian former boyfriend against their convictions for the killing of British student Meredith Kercher took a sensational turn on Wednesday when independent, court-appointed experts dismissed as unreliable forensic evidence crucial to the prosecution case.
Two Rome university professors said there was no certainty that traces of DNA found on the alleged murder weapon belonged to Kercher.
They added that the vital piece of evidence which linked Knox's ex-boyfriend, Raffaele Sollecito, to the scene of the murder – a trace of his DNA on Kercher's bra clip – could have got there by contamination, as the defence maintained at the trial.
The breakthrough for the appellants came just two days after their case suffered a hefty setback.