How can you convict her of murder when there's this:
Nick Squires of The Daily Telegraph reported that Guede "...became a suspect in the murder two weeks after Miss Kercher's body was found, when DNA tests on a bloody fingerprint and on samples taken from the body were found to match samples which police already had on file following his earlier arrests."[54] A manhunt for a fourth suspect began on 19 November 2007 after a bloody handprint found on Kercher's pillow was matched to Guede. Guede had left Perugia by train a few days after the murder. Interpol had traced a computer that he had used in Germany to access Facebook and reply to a message from a Daily Telegraph journalist. In his message, Guede had said that he was aware that he was a suspect and wanted to clear his name. On 20 November 2007, the Bundespolizei arrested Guede on a train near Mainz, where he was apprehended for travelling without a ticket. When questioned, he stated that he was returning to Italy to give himself up. He was extradited to Italy on 6 December 2007.
DNA matching Guede's was found both on and inside Kercher's body and on her shirt, bra and handbag. A bloody handprint found on a pillow under Kercher's back was also matched to Guede. The prosecution argued that a severed piece of Kercher's bra, including its metal hooks, revealed traces of both her DNA and that of Sollecito. Knox's lawyers later argued that DNA evidence had been contaminated during the investigation at the crime scene and when the investigators accidentally moved the evidence during the 47-day delay in retrieving the samples. A June 2011 report by court appointed forensic experts concluded that there was not enough DNA on the bra clasp to retest, that the collection of the bra clasp evidence did not conform to internationally accepted procedures, and the collection was "in a context that was highly suggestive of ambient contamination".
http://en.wikipedia.org/wiki/Murder_of_Meredith_Kercher#Guede.27s_arrest
So I'm not surprised she has been freed.