She created multiple lies about what happened that night. One of those lies was that she was there when the murder and sexual assault happened when another man did it, who we now know was completely involved.
I think you mean uninvolved, and Knox made that statement only after 36 hours of intense interrogation by the police.
However, her initial statement was that she spent the entire night with her boyfriend (for the first time). He was being interviewed at the same time and said she did not spend the night with him.