Answer:
Eyewitnesses confidence is only weakly related to eyewitness memory.
Explanation
This happen because when humans perceive a certain a situation, we will record it based on the pre-determined schema that we already have in our head.
So, when different eyewitnesses saw a crime event, the memory that they have tend to be different from one person to another. This make their confidence over the recollection very weakly related to their memory.