A written document containing factual information about an event is called a:

A written document containing factual information about an event is best described as a police report or incident report (often abbreviated as IR). This type of report typically contains details such as the date, time, location, involved parties, and a narrative describing the events that took place. Police reports serve as a formal record that can be used in investigations, court proceedings, and other legal contexts. They are essential for maintaining accurate and comprehensive documentation of law enforcement activities.

In contrast, a case summary usually provides an overview of the facts and findings of a case rather than detailed accounts of events. A statement typically refers to an individual's account or testimony regarding an event but may not encompass all the necessary factual elements. An incident log, while it records specific events, is generally less detailed than a police report and may simply track occurrences without the comprehensive narrative required for legal documentation. This clarity and thoroughness in documenting events is what distinguishes a police report as the correct answer.