In science, a fact is something for which evidence can be shown. For example, I once had to learn how to do fire investigation.
I learned that one did not have to set a fire and watch it burn down a house to know how the house burned.
One merely has to be able to find evidence for what happened, not necessarily repeat what happened.
This is why the scientific method is about observation, not just experimentation. Many sciences, like forensics, geology, astronomy, meteorology, etc. do very well without experimentation, by observing evidence.