The hair by itself, like Steve’s photo, needed to be combined with other evidence to become more persuasive.
So, Scott Peterson didn't get sentenced to death based on one piece of hair after all?
Most of the other evidence was highly circumstantial and there was evidence manipulation and problems with the jury in that case as well. The prosecution argued that Laci's hair could only have gotten on the boat after her death as she was never near that boat while alive. However, a police officer was found to have excluded from his report that a witness he talked to had said that she saw Laci near the boat a day before her death. Apparently, the jury did not find that a big deal.
In court, things are very seldomly black and white.
As far as circumstantial cases go, what it basically means is that the prosecutor is using (very often) scant physical evidence to tell a story that might convince the jury. Very often the pieces of physical evidence can be interpreted in more ways than one which also allows for a different story to be told using the same evidence.
I think I understand what you are trying to say, but just in case I am wrong, why don't you tell us in simple terms what point you are trying to make?