Which factor would necessitate a show up procedure for suspect identification?

A show-up procedure is a form of suspect identification where a witness is presented with a suspect shortly after a crime has occurred. This method is used primarily to confirm whether the person identified is indeed the perpetrator, and it is particularly relevant in situations where immediate identification is necessary.

The correct choice highlights that when there is a need for immediate display to witnesses, the urgency of the situation may require law enforcement to conduct a show-up to quickly ascertain whether the suspect is the person the witnesses saw committing the crime. This swift identification can be crucial in criminal investigations, especially to prevent the potential loss of witness reliability over time or in case the suspect might be able to escape.

The context of the other options further clarifies why they do not fit the criteria for necessitating a show-up procedure. For instance, a clear description provided by witnesses or a prior arrest could serve as auxiliary information but does not inherently justify the need for an immediate show-up. Additionally, if witnesses are unavailable, conducting a show-up loses its intended purpose, as the identification would not occur in the required context of immediate witness interaction.