Indirect evidence is interesting. Sometimes, it's almost as conclusive as direct evidence and sometimes it's not conclusive at all. It really depends on the specific circumstances.
I really like the example in the article about a woman who saw someone leave a store with a gun and was told that it was just robbed. Even though she never saw the person actually committing the crime, the things that she did see when combined, are almost as conclusive as indirect evidence.
I think we can infer from all this that it's extremely important for witnesses to testify with every detail they remember and as accurately as possible. It's usually the details that makes one piece of indirect evidence more reliable than another.