Archaeologists directly observe artifacts. For example, there's a class of artifact that have been called "storage jars" but there wasn't any evidence of what was "stored" in them. Some hypothesized that they were used as chamber pots, but they're too large to sit on. Recently, an archaeologist
directly observed the eggs of a human fecal parasite inside of such a "storage jar," evidence in favor of the chamber pot hypothesis. They further
hypothesize that these "storage jars" were housed in a wooden frame so that people could sit & do their business -- an ancient port-a-potty -- with little expectation that such a wooden structure would have survived the millenia. And, note the title "ceramic pot was
probably a portable toilet."
https://arstechnica.com/science/2022/02/this-ancient-roman-c...
The criminal justice system works in the same way. Detectives look for evidence that a person was at the scene of a murder, and evidence linking the person to the murder weapon, and establish guilt beyond a reasonable doubt even though no other living person directly observed the murder.