The strange thing about many high-profile legal cases is they end up a matter of public perception. A great legal novel by Zola, La Bete humaine, tells the story of two men, one a monstrous loathesome brute and a morally upright citizen who is well-liked and respectable. Of coarse the well-respected man commits a heinous murder but the public is too willing to condemn the brute who is accused of the murder.
The facts seem to support another murderer and Amanda Knox was in the wrong place at the wrong time. She was weird, involved in drugs and maybe some weird sex, but that does not mean she murdered her roommate.
I recall visiting a couple, friends of my sister, and they ranted and raved on how evil and guilty Amanda Knox was. They were among those who just did not like her. Nobody ever had proof of anything- it was all supposition and far too subject to opinion and perception.
Psychologists say 1 out of 10 people have psychopath tendencies. So if any murder suspect has a 1 in 10 chance of being a psychopath, that 1 out of 10 person is going to be perceived as guilty based on their actions. Even innocent people with psychiatric issues will act strange and this will automatically draw suspicion on them. Some people act with callous indifference at the death of a friend or family member- but if it were a murder victim, that callousness will draw suspicion. "When he learned his wife had been murdered, he had no reaction. Not even a tear. Must be guilty!" Not necessarily.