[nvrspyx]

I think this is unnecessarily pedantic. If the crime was over a prolonged period of time or on multiple instances with the same witness present, then you eventually become familiar with the perpetrator.

The original commenter obviously meant that a witness should be reasonably familiar with the person, whether that be from knowing the person prior to any crime or, in rare cases like kidnappings/torture/etc., during the prolonged period of time with the accused. It's not like we're writing legislature ourselves here; those rare cases probably just didn't come to mind when the original commenter wrote their comment. Informal internet commentary need not be so needlessly scrutinized.

But if we really want to be pedantic with your example, you would become familiar with the person from the "previous" torture sessions.