The correct answer is: It can be proven using objective evidence.
To be<em> factual</em> is to use or consist of facts, meaning the information provided can be proven and its characteristics are not altered by external interpretations (opinions from others).
Just as facts, <em>objective evidence</em> can be proven by observation and analysis. Regarding the excerpt, it can be proven that Hossack was struck at the head by analyzing his corpse, and that the crime took place "a few miles out from Bedford" by visiting the crime scene.
