The "doubt" is considerably lessened when there is a plethora of such evidence.
Exactly..
It's like money. Some evidence is "worth" substancially less than other evidence.
If it's worth less, then you need more of it.
So what would you rather have? An eyewitness who can't see very well in the dark from a car parked across the street ...and can't tell the difference between two black men? Or a strong circumstantial case?
The answer is that a circumstantial case can be just as strong as direct evidence.