What is a line-up filler?

A line-up filler refers to an individual who is included in a police line-up but is not a suspect in the crime being investigated. The purpose of line-up fillers is to create a group of individuals that the eyewitness can view, allowing them to determine if they can identify the perpetrator.

Including fillers who closely resemble the suspect in appearance helps ensure that the identification process is fair and reduces the chances of misidentification by the witness. In this context, fillers are essential for maintaining the integrity of the identification process, as they provide a visual context that makes it more difficult to highlight the actual suspect unduly.

Witnesses only identify the suspect if they see them among the fillers, making the line-up a critical tool in criminal investigations. Thus, this option correctly describes the role of a line-up filler in the identification process.