Suppose we say that the investigators of the Kercher murder privileged the hypothesis that Knox and Sollecito participated in it. Once convinced of it, those investigators went looking for every little thing that seemed to support it, even while the murder premises were all but shrieking: "Guede did it; case closed." That has nothing to do with Knox's story-changing. Whether the interrogation of Knox would have proceeded differently if the investigators had not been privileging the hypothesis, Knox gave different stories, one of which included a false accusation. Once she did that, the story-changing itself became a legitimate focus of concern. To put that another way: One can say, "If the investigators hadn't privileged the hypothesis that Knox participated in the murders, the story-changing wouldn't have occurred." Maybe so--but they did privilege it, and the story-changing did occur. That is as much a part of reality as the DNA in that room.

Since the false accusation, or rather, the statement that she had an impression that Lumumba had some association with the crime, which is what Knox provided, was itself almost certainly due to pressure from the police to give exactly that testimony, then it seems more than a little unreasonable to hold her accountable for "story changing." The only reason that Knox pointed to Lumumba was that the police pointed her to him.

Suppose that you were living in a rather more paranoid country, where the government suspected you of subversive activities. So, they took a current captive suspect, tortured them, and told them they'd stop if the suspect accused you. If the suspect caved, would you blame them for accusing you, or the government for making them do it?